Applied Science, Faculty of
Electrical and Computer Engineering, Department of
DSpace
UBCV
Abar, Vanesa Mirzaee
Master of Applied Science - MASc
University of British Columbia
Electronic versions of historical documents are traditionally limited in both the representations they allow as well as the level of computational manipulation they support. Most electronic documents have two minimal advantages over their hard-copy printed counterparts: availability and keyword search. This means that electronic versions of printed matter do not allow the search for concepts, or the relations between concepts, found within a document. In this work, we present a novel approach to this issue by using ontologies to represent the semantics of the knowledge contained in historical documents. We utilize an evolving methodology to design and build an ontology to represent the information in the book, "The History of the Iranian Constitution. " After a review of available ontology development environments, we selected Protege-2000 to formalize and instantiate our ontology. The ontology was later evaluated by utilizing a set of competency questions and motivating scenarios. Our implementation was successful in answering these questions as well as in providing support for the selected scenarios. Our implementation and the evaluation results are presented along with our proposed future work.
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Abstract 11 Abstract Electronic versions of historical documents are traditionally limited in both the representations they allow as well as the level of computational manipulation they support. Most electronic documents have two minimal advantages over their hard-copy printed counterparts: availability and keyword search. This means that electronic versions of printed matter do not allow the search for concepts, or the relations between concepts, found within a document. In this work, we present a novel approach to this issue by using ontologies to represent the semantics of the knowledge contained in historical documents. We utilize an evolving methodology to design and build an ontology to represent the information in the book, "Tfte History of the Iranian Constitution. " After a review of available ontology development environments, we selected Protege-2000 to formalize and instantiate our ontology. The ontology was later evaluated by utilizing a set of competency questions and motivating scenarios. Our implementation was successful in answering these questions as well as in providing support for the selected scenarios. Our implementation and the evaluation results are presented along with our proposed future work. Table of Content ; i i i Table of Contents Abstract ii Table of Contents i i i List of Tables v List of Figures vi 1 Introduction 1 1.1 Problem Statement and Motivation 1 1.2 Thesi s organization , 4 2 Background and Related Work 6 2.1 Related Work 6 2.1.1 Model Edition Partnership (MEP) proj ect 8 2.1.2 Historical Event Markup and Linking (HEML) project 8 2.1.3 Analysis of these approaches and our selected approach 10 2.2 Knowledge Representation and Ontologies 12 2.2.1 Why ontologies? 13 2.2.2 Defining the term "ontology" 16 2.2.3 What do ontologies look like? 19 2.2.4 Ontology classification 22 2.2.5 Methods for building an ontology 28 2.2.5.1 Uschold and King Methodology (Enterprise Methodology) 30 2.2.5.2 Gruninger and Fox Methodology (TOVE Methodology) 37 2.2.5.3 Uschold and Gruninger Methodology (Unified Methodology) 43 2.2.5.4 Gomez and Fernandez Methodology (METHONTOLOGY) 45 3 Methodology 54 3.1 Selected Approach 54 3.1.1 Identify the purpose, scope, and intended users 56 3.1.2 Ontology Building 58 3.1.2.1 Domain analysis and knowledge acquisition 58 3.1.2.2 Investigate the possibility of using an existing ontology 59 3.1.2.3 Building an informal ontology model 60 3.1.2.4 Building a formal ontology model 61 Table of Content iv 3.1.2.4.1 Selecting a development tool 62 3.1.2.4.2 Protege-2000 68 3.1.3 Ontology Evaluation 80 4 Build a history ontology 81 4.1 Identify the purpose, scope, and intended users 81 4.2 Ontology building 85 4.2.1 Domain analysis and knowledge acquisition 85 4.2.2 Building an informal ontology 88 4.2.3 Building a formal ontology model 105 4.2.3.1 Mapping our domain concepts to a class hierarchy 105 4.2.3.2 Assigning properties to classes (attributes & relations) 107 4.2.3.3 Defining Constraints 122 4.2.4 Ontology Evaluation 123 5 Conclusions and Future Work 139 5.1 Summary of thesis and results 139 5.2 Conclusions 140 5.3 Future Work 140 Bibliography 142 List of Tables v List of Tables Table 2-1 Enterprise Ontology Terminology 36 Table 3-1 a general description and design features of the tools within the Onto Web framework (based on the work in [WebOnto 2002]) 63 Table 3-2 Usability features supported (WebOnto framework) 63 Table 3-3 Inference services provided by the tools (WebOnto framework) 64 Table 3-4 Interoperability, knowledge representation, and methodological support comparison (adapted from [WebOnto 2002]) 65 Table 3-5Evaluation framework of the WonderTools Project 66 Table 3-6 Summary of the results obtained in the WonderTools Project 67 Table 3-7 Slot widgets in Protege-2000 70 Table 3-8 Storage back-end plug-ins in Protege-2000 70 Table 3-9 Tab plug-ins in Protege-2000 71 Table 4-1 First draft of the competency questions 83 Table 4-2 Motivating Scenarios 84 Table 4-3 Competency questions related to the notion " P L A C E " 85 Table 4-4 Competency questions related to the notion " E V E N T " 86 Table 4-5 Competency questions related to the notion "PERSON" 86 Table 4-6 Competency questions related to the notion " D O C U M E N T " 87 Table 4-7 Partial view of the glossary of terms 88 Table 4-8 Concept dictionary related to the notion " P L A C E " 90 Table 4-9 Concept dictionary related to the notion "PEOPLE" 91 Table 4-10 Concept dictionary related to the notion " E V E N T " 91 Table 4-11 Concept dictionary related to the notion " D O C U M E N T " 92 Table 4-12 Concept dictionary related to the notion "TIME" 93 Table 4-13 Mapping between the terminology we used and Protege-2000 terminology 105 List of Figures yi List of Figures Figure 2-1 A sample document using H E M L representation language 10 Figure 2-2 Merging different ontologies 14 Figure 2-3 Integrating several ontologies into one more general ontology 15 Figure 2-4 Partial view of a simple newspaper ontology (concept/sub-concept relations) 21 Figure 2-5 Partial view of the newspaper ontology (relations amongst concepts) 21 Figure 2-6 Constraint imposed on concept property within the newspaper ontology (axiom) 22 Figure 2-7 C Y C ontology 23 Figure 2-8 Sowa's ontology 23 Figure 2-9 U M L S 25 Figure 2-10 TOVE 25 Figure 2-11 Example of application ontology 26 Figure 2-12 Part of the frame ontology in Ontolingua 27 Figure 2-13 Uschold and King Methodology (Enterprise Methodology) 31 Figure 2-14 Gruninger and Fox Methodology (TOVE Methodology) 38 Figure 2-15 TOVE Ontologies 41 Figure 2-16 TOVE organization concept taxonomy 42 Figure 2-17 Part of hierarchy of roles in organization ontology (TOVE)'. 42 Figure 2-18 Gruninger and Uschold Methodology (Unified approach) 44 Figure 2-19 M E T H O N T O L O G Y ontology life cycle 48 Figure 2-20 Ontology requirements specification document for the Chemical ontology 50 Figure 2-21 Part of the Chemical ontology 51 Figure 2-22 Water-fall, iterative, and evolving approach 52 Figure 3-1 Our Ontology Development process 55 Figure 3-2 Results for ease of use comparison of the selected tools (WonderTools project) 66 Figure 3-3 Screenshot of the Protege 2000 development environment 72 Figure 3-4 Slots in Protege-2000 73 List of Figures vii Figure 3-5 Facets in Protege-2000 74 Figure 3-6 Defining axioms in Protege-2000 76 Figure 3-7 A knowledge acquisition form in Protege-2000 77 Figure 3-8 Meta Class " :STANDARD C L A S S " in Protege-2000 78 Figure 3-9 An example of user-defined meta-class in Protege-2000 79 Figure 4-1 Main concepts within our ontology 94 Figure 4-2 Overview of main concepts and relations in our history ontology 95 Figure 4-3 Time model in our domain 96 Figure 4-4 A C A L E N D A R D A T E within our history ontology 97 Figure 4-5 Interrelations amongst concepts related to " P L A C E " 98 Figure 4-6 Relations between the concept " P L A C E " and other concepts within our ontology 99 Figure 4-7 Concept hierarchy for "AGENT," "PERSON, ""GROUP OF PEOPLE," and " C O U N T R Y " 100 Figure 4-8 Relations between "PERSON" and "GROUP OF PEOPLE" and other concepts in our domain 101 Figure 4-9 Time-based hierarchical relationship between a PERSON and POSITION 102 Figure 4-10 Conceptual model for position hierarchy 102 Figure 4-11 Interrelations amongst events 103 Figure 4-12 Association of an " E V E N T " with other concepts in our domain 104 Figure 4-13 Concept " D O C U M E N T " and its relation with other concepts in the domain 104 Figure 4-14 Our ontology class hierarchy in Protege-2000 106 Figure 4-15 Inheritance of properties and relations by subclasses 107 Figure 4-16 Reification of the relation MEMBERSHIP as a concept 109 Figure 4-17 An instance of the reified relation "MEMBERSHIP" 110 Figure 4-18 Reification of the relation RESIDENCY as a concept 110 Figure 4-19 An instance of the reified relation RESIDENCY I l l Figure 4-20 Reification of the relations BIRTH-PLACE and D E A T H - P L A C E as concepts 112 Figure 4-21 An instance of the reified relation D E A T H - P L A C E 113 List of Figures viii Figure 4-22 Reification of the relation TITLE-OF-HONOR as a concept 113 Figure 4-23 A n instance of the reified relation TITLE-OF-HONOR 114 Figure 4-24 Reification of the relation I N V O L V M E N T as a concept 114 Figure 4-25 An instance of the reified relation I N V O L V E M E N T 115 Figure 4-26 Modeling the temporal place hierarchical organization 117 Figure 4-27 Class implementation of main place concepts in Protege 118 Figure 4-28 Reified relations used to represent the temporal dynamic organization of places in Protege 118 Figure 4-29 An instance of the place hierarchy in Protege 119 Figure 4-30 Reified relations used to capture the dynamicity of the POSITION hierarchy 120 Figure 4-31 Implementation of reified relations for position in Protege-2000 121 Figure 4-32 A n instance of the reified relation POSITION-HIERARCHY and HOLDS-POSITION in Protege-2000 122 Figure 4-33 Using Protege-2000 built-in query engine to answer competency questions 124 Figure 4-34 Using the P A L query engine to answer competency questions 125 Figure 4-35 "Knowledge Tree" visualization of the place hierarchy for "Iran" 126 Figure 4-36 Using TGViz visualization tab to browse the hierarchy of places related to country "Iran" 127 Figure 4-37 Results for Competency Question #1 129 Figure 4-38 Results for Competency Question #2 130 Figure 4-39 Results for Competency Question #3 131 Figure 4-40 Results for Competency Question #4 132 Figure 4-41 Results for Competency Question #5 133 Figure 4-42 Results for Competency Question #6 134 Figure 4-43 Results for Competency Question #7 135 Figure 4-44 Results for Competency Question #8 136 Figure 4-45 Results for Competency Question #9 137 Figure 4-46 Results for Competency Question #10 138 Acknowledgements First of all, I would like to offer my sincere appreciation to my supervisors Dr. Babak Hamidzadeh and Dr. Lee Iverson. I am deeply grateful for their valuable guidance and insightful ideas throughout the entire project. I would also like to thank Dr. Philippe Kruchten for his valuable feedback and opinions as a member of my committee. I shall make a special thank to Doris Metcalf and Darija Tomasic in the ECE department for their help and support. Many thanks to my fellow grad students in the U C L Lab. Most importantly I would to thank my family and friends for their everlasting support. Last but not least, I would like to thank my dear Mario for his love, friendship and his patient support. I have no doubt that without his help I could not go this far. Vanesa Mirzaee Abar University of British Columbia January 2004 To my mother Chapter 1. Introduction 1 Introduction 1 1.1 Problem Statement and Motivation Over the last two decades, we have witnessed the dawn of digital documentation. Electronic versions of traditionally printed matter offer different individuals with diverse interests the opportunity to access a wealth of information in a simple manner. When the knowledge found in these printed documents is captured in electronic forms, additional tasks can be performed on it than is possible with traditional hard-copy versions. The main advantage that the electronic medium provides is the possibility of searching and manipulating the information in innovative ways. With an electronic document, a search is not limited to the index provided by the author or publisher at the back of the book or end of the article. However, current electronic versions of text documents have certain characteristics that impose limitations when we try to represent, access, search and manipulate this information. Computational representation of knowledge: electronic information exists mostly in natural language text format [Alani, Kim et al. 2003].This type of information is not well suited for representations that allow capturing anything more than words without meaning. In other words, it cannot be easily computationally manipulated. Repetitiveness: Information found in electronic forms is usually repetitive. A lot of material related to a particular subject may be found, but often different sources disagree on the structure used to represent it. A good example of this repetitiveness of information is seen in historical biographies. We may find dozens of different books or websites referring to Princess Diana, all of these portraying nearly the same information, but in different forms. Reuse and Sharing: Many times, the existence of repetitive information is due to the particular format used to represent the available information. Currently, available data is structured in a manner that does not facilitate its reuse, which leads to this repetitiveness. This might be avoided if we had an efficient model to refer to existing information elsewhere [Swartz 2002]. Chapter 1. Introduction 2 Underutilized affordances: Traditionally, we assume that a document or article will be read in a sequential manner, as has been done since the advent of writing. Up to now, it has been assumed that the main advantage of electronic formats over printed matter is the convenience of being able to find the material without having to physically attain it from a library or other repository. Once we have this information in a digital format, it is unclear as to how the user might interact with this information besides being able to print it and/or read it. New technology has the potential to provide us with additional functionality over traditional printed matter [Hockey 1999]. When the information is stored electronically, it can be organized in many different ways, presented in different formats (graphs, charts, etc.) and used for a variety of purposes, only one of which is creating a printed publication. The additional possibilities that this medium provides for capturing and representing knowledge give the user an opportunity to interact with this knowledge in innovative ways. Searching for semantic: The Internet provides us with a large amount of easily accessible information. However, this information can be rendered useless i f we do not possess the appropriate tools or methods to utilize and understand it. With existing search engines, it can sometimes be difficult to find a document with the desired information one seeks. Even i f we do find this document, it can still be hard to find a particular subject or specific information within the document. In the event that an appropriate document is found and that the specific area of interest within the document is pinpointed, it is still not easy to capture the semantic within this document. Currently, available paradigms representing electronic versions of documents lack an understanding of the semantic within these documents [Palmer 2001]. Queries within a document are usually limited to key-word searches. Relations between concepts within a document cannot be found by using a keyword search; we are only able to find the instances of the concepts contained in the document. For example, two instances, person X and person Y can be easily queried by keyword search; however, unless users read at least some parts of the document, they can not determine whether these two people are related to each other, how this relationship is defined, and during what time period this relationship holds. Chapter 1. Introduction 3 Given the time and effort invested in creating electronic information and how sharing of this information has been widely adopted throughout the world, it makes sense to pause and think about these issues and try to find paradigms to better represent and allow access to the available knowledge. The work presented in this thesis tries to address the issues we have introduced so far in the specific domain of historical information. A wealth of historical information has been transmitted into electronic form. This representation of historical data suffers from all the aforementioned limiting characteristics. In particular, narrative history texts contain certain elements that characterize the genre; they are usually organized along a time line and share similar key concepts such as people, places, events, and so forth. These texts share another significant similarity: they are all about events that take place in the past. Additionally, for any given period of time, these texts are not densely populated. Typically, these electronic collections are available in text or Hyper Text Markup Language (HTML) data forms exclusively. This is unfortunate since text and H T M L data cannot be computationally manipulated in an effective manner. Considering the characteristics of historical knowledge currently available in an electronic format and the shortcomings of traditional methods used to represent this knowledge, we propose a paradigm in which the semantics and meaning behind the words in a historical text can be captured and represented. The main goal of this project is to explore the possibility of capturing the meaning (the semantic) behind the words in a natural language history text. We propose a new conceptual paradigm for representing and formulating documents of a historical nature. Our purpose is to develop a conceptual model that not only represents the content of a historical document, but also illustrates its meaning. In order to capture the semantic, temporality, and dynamicity of this knowledge, we have chosen to use an ontological approach. This approach is used to represent and formulate knowledge in a manner that allows it to be computationally manipulated, shared and reused amongst different applications. Ontologies are conventionally used for semantic-based information Chapter 1. Introduction ; 4 representation and retrieval. Additionally, they can capture the semantic of the concepts to be represented or searched for. An ontology is a conceptual model, a resource containing knowledge about "concepts" that exist in the world and how they relate to each other. A concept is a symbol for representing meaning with well defined attributes and relations with other concepts [Mahesh 1996]. An important characteristic of the proposed ontology model is its ability to represent a temporally dynamic hierarchy of concepts. This is of particular importance with historical data, since the concepts and the relations between them change and evolve through time. Two concepts related to one another at a certain point of time may not be related to it at another time stamp. Additionally, this model not only captures the relationships between the concepts but also demonstrates the interrelated hierarchal structure within them. The temporal features of this ontology will enhance our semantic model, since they will allow us to capture the time dimension of the existing relations. This temporal representation gives the relations more realism approaching that which they have in the real world. 1.2 Thesis organization The remainder of this thesis is organized as follows: • In Chapter 2, Background and related work, we introduce the state of the art in research related to representation of historical information in electronic formats. This research has been mostly carried out by communities interested in the field of the humanities. This is followed by an introduction to our selected approach "ontology engineering approach." This includes an overview of terms and definitions of key concepts in the field, motivation to use ontologies, ontology classification along with examples of different types of ontologies, and an in depth discussion and analysis of several ontology building methodologies. • In Chapter 3, we describe our chosen methodology. A detailed explanation of the methods and techniques we adopt and use to build our conceptual model (ontology) is provided. This is followed by a presentation of a survey of existing ontology Chapter 1. Introduction 5 development tools. As a result of this investigation, we choose Protege-2000 as the application for building our formal ontology. An in depth description of Protege, its features and characteristics is provided as well. • In Chapter 4, we explain the procedure undertaken for building a history ontology based on the guidelines described in Chapter 3. The procedure include a description of the domain that the ontology is intended to capture, identifying the purpose, scope, and intended users of the ontology, defining the ontology building process, utilization of the tool, evaluating the resulting ontology and analyzing the experimental results. The results obtained for each step of our ontology development are presented after each stage. • In Chapter 5, we present our conclusions and proposed future work. This includes a summary of the thesis, its main contributions and results obtained. Chapter 2. Background and Related Work 6 2 Background and Related Work In this chapter we first introduce the state of the art of research relating to representing and manipulating historical information in electronic formats. Two examples of current research projects in this area are presented (MEP and HEML) . This is followed by a discussion of the virtues and shortcomings of existing approaches for representing historical information in a manner that both captures the semantic behind a document and allows its reuse and sharing. This discussion is followed by the introduction of our selected approach to represent historical knowledge: "ontology engineering." We proceed to explain our selected approach in detail by presenting an overview of the terms and definitions of key concepts in the field, our motivation to use ontologies, a detailed ontology classification with examples of different types of ontologies, and an in depth discussion and analysis of several ontology building methodologies. 2.1 Related Work A wealth of historical information has been encompassed in electronic forms and is available through several different resources such as digital libraries. Most of the research relating to these historical documents, or for that matter, documents in any other humanity area, deals with how to create digital copies of these documents and store them in repositories in a manner that facilitates later access to them. This digital media usually integrates meta-data or a notation which provides information about its content [Burchardt 2001]. The major functionality that these electronic documents using meta-data or other types of notation provide is the facility to retrieve the best-matched document to any search request. Many researchers from different fields are involved in projects that try to address these and related problems; this is an active area of research [Hockey 2000]. An example of one such research projects is the Art and Humanities Data Service (AHDS) History project (HDS), which aims to provide a guideline for creating, describing, using and preserving historical digital resources [AHDS; HDS]. The HDS is funded by the Joint Information Systems Committee (JISC) of the U K Higher Education Funding Councils to collect, catalogue, manage, preserve and encourage the re-use of historical digital resources. Chapter 2. Background and Related Work 7 This committee provides guidelines on the following: • Collecting and preserving historical digital resources • Providing access to collections of historical digital resources held by different organizations • Developing online data and metadata delivery systems to enhance access to these collections • Promoting standards in the creation, description, use and preservation of historical digital resources Assuming that all this historical knowledge preserved in an electronic format is available for retrieval, two questions arise: what happens after retrieving this information? What will the user do or want to do with these documents? It is reasonable to assume that a user might wish to obtain the semantic behind the words of these documents. Obtaining this kind of information traditionally requires the user to read the document (or at least some part of it). It would be ideal for electronic historical documents provided methods and techniques of posting these types of historical questions, such as those dealing with relationships between characters named in the historical document, the connections between events, the location of these events, the hierarchy of governmental positions at any given time, the changes that these hierarchies undergo throughout time, etc. The common approach utilized to representing this type of knowledge (inside a historical document) uses mark-up languages such as Standard Generalized Markup Language (SGML) and Extensible Markup Language (XML), which tag the information within the document. To the best of our knowledge, there are no current projects in the research community that focus on generating a representation addressing similar interests similar to our. However, we do find two projects that utilize ideas somewhat similar to ours, although taking different approaches. These projects are presented in the following sections. Chapter 2. Background and Related Work 8 2.1.1 Model Edition Partnership (MEP) proj ect The MEP project involves editors from seven different editorial projects in the history domain. Two of these projects are designed to aid in creating image editions, and the other five help prepare letterpress publications. These documentary editions provide the basic source material for the study of American history, by adding the historical context which makes the material meaningful to readers. Documentary editors prepare the material for publication by transcribing the documents, organizing the sources into a coherent sequence which tells the story (the history) behind them, and annotating these documents with information to help the reader understand them [Hockey 1999]. The goals for this partnership are to developed frameworks for electronic historical editions, to develop computational approaches to create new editions and to provide a series of models and guidelines to be shared amongst editors while preparing the material for publication [Chesnutt 1995]. In this work, a series of models were developed to transform historical documents to electronic versions. This project employs S G M L to support access to the information that exists within the documents. This is done by developing a set of S G M L Document Type Definitions (DTDs), which define a markup system for publishing historical documents [MEP 2003]. 2.1.2 Historical Event Markup and Linking (HEML) project Another project related to our work is the H E M L project. This project proposes a markup scheme to be used for electronic representation of historical events on the web. In this work, X M L tags are defined to describe historical events [Robertson 2003]. H E M L defines a lightweight X M L language that associates web resources with historical events described in terms of time, location, and participants. Figure 2-1 presents a sample of a document that has been transformed into H E M L language. The goal in developing H E M L is to use this scheme as a framework to tag documents that record historical events, their date and location. This facilitates assembling a computerized collection of information and associating it with the document. It then Chapter 2. Background and Related Work 9 becomes possible to search for a description of events on a certain day, or in a certain region amongst collections that share this same scheme [Robertson 2001]. According to the H E M L scheme an event is composed of the following: 1. A label to name the event 2. One or more keywords that group conceptually similar events 3. A location in which the event takes place 4. A 'chronology' of the event, describing the time in, or during which, the event takes place 5. A list of people or groups of people who participate in the event 6. A list of evidence for the event, either in physical form (such as printed books or 16mm film) or as a web resource Chapter 2. Background and Related Work 10 van Beethoven - Biography - Microsoft Internet Explorer He Ed* View Favorites look Help Q&x*. ' x" 2^ \ Search • •• ^http;/j^.mta,ta/hemi<ocoofysar^xhtllil Google- ibrucerobertwi + heml v Wlwt Is This? Table ivrellne Mac Ammatea Map xfitn^fteiti source Locations Bom Helifigenstadi: feprttz (rr*od, 7epHcs| (Search Web • home Favorites ^jf* Media & 1 14 blocked Ludwiq van Beethoven BIOGRAPHY This document was converted to xhtml /mm an html original at hUp:l'horm.swipnet.se/zabonldcultur/ludwig/beelbio.htm and hand :Eveat element wen added as indicated below. Its author, Pelle Ostberg. has kindfy agreed to Us use in the Heml project H e w a s b o m In the G e r m a n t o w n of B o n n on the 16th of December m0yj£ His grandfather Ludwig and his father Johann were both musicians. Johann was to act as little Ludwig's first music teacher, but •«.: otv&msiw* - 0 !W~?gfc »««»«»•> 0 Kvcwt Date l.otsiiion A D 1770 December 16 Bomt ftettitoven Moves T o A D 1792 Vienna A D IWZ October 6 Hedi.ijeJiKt.Klt - r; ^ o r g a n i s t C. G. Neefe, Passing eleven r Neefe, and at twelve had his first Neefe's assistant until 1787, when at . Even though Vienna was to be his t visit was short. On heanng that his Jed to Bonn. Five years later he finally 0 live and wor te^^ 1 in 1792<liNf^tudied composition and itupe^FHaydn, Schenk, Salieri and fger. At the same time, he tried to elf as pianist and composer, His good - n U I robertson £ heml nks # Internet Figure 2-1 A sample document using HEML representation language This figure illustrates a document in which HEML markup language has been used. By choosing the HEML links within the document a new pop-up window which demonstrates the date and location that is associated with the event is shown (adapted from http://heml.mta.ca/heml-cocoon/sample-xhtml) Although this reperesentation does allow a certain amount of the knowledge contained in a history document to be captured and represented, it lacks and understanding of the semantic within the document or the rich relations between the concepts. 2.1.3 Ana lys is o f these approaches and our selected approach Our goal of developing a paradigm to represent semantic knowledge within historical documents is unattainable with the approaches proposed in these and other similar projects. The current preferred approach for creating information infrastructures such as those presented in the last two projects is to use markup languages. Amongst these markup Chapter 2. Background and Related Work 11 languages, X M L is the most popular choice. However, X M L can only represent the syntax within a document, not the semantic. This means that the tags in an X M L document are semantic free. That is, these tags do not have any predefined meaning; they do not represent the semantic, meaning, or behavior of concepts in the document and only present content and structure [Jarrar 2000]. These projects use X M L as an exchange format. However, an X M L document by itself is not completely useful for our purposes. Associating semantics to these tags requires additional mechanisms to describe the behavior and the meaning for the concepts within a document. This association cannot be made unless there is a consensus amongst people within a community interested in a specific domain on what these semantics are [Spyns, Meersman et al. 2002]. In addition to this, In order to capture the dynamicity of the information in a historical document, we require additional functionality that to which is attainable by using markup languages such as X M L . An ontology is the basic building block used to define richer relationships between different concepts. It allows members of a community of interest to establish a joint terminology, which enables greater flexibility and helps achieve reusability and sharing of knowledge. Ontologies are often used to represent a specification of domain information by providing a consensual agreement on the semantic of the knowledge that the domain is aimed to express [Spyns, Meersman et al. 2002]. Another motivation behind using ontologies is that they allow for sharing and reuse of knowledge in a computational representation. Based on these characteristics inherent to ontologies, we choose an ontological approach to represent the history domain we intend to capture. From the general point of view, the issues discussed in this thesis can be situated within the Knowledge Representation (KR) area of Artificial Intelligence (Al), and more precisely, within what is called ontology-based knowledge representation. Therefore, the rest of this chapter gives an overview of the research done in the A l community in the fields of knowledge representation with a specific emphasis on ontology design methodologies and techniques. Chapter 2. Background and Related Work 12 2.2 Knowledge Representation and Ontologies Over the past three decades, researchers have spent an enormous amount of effort to collect and represent knowledge about the real world in forms, which can be easily manipulated computationally. The Artificial Intelligence (Al) Community is actively involved in studying the issues related to this field. Knowledge Representation is a branch of A l . This field refers to the study of how knowledge can be appropriately represented in computational models and what kinds of reasoning can be done with that knowledge. John F. Sowa [Sowa 2000a] defines Knowledge Representation (KR) as analyzing knowledge in some domain and transforming its informal specification to a computable model. Generally speaking, in order to capture the formal specification of knowledge, one must follow these steps [Sowa 2000a]: • Identify the kind of things that require representation • Provide an informal specification of these things • Map the informal specification to a computable form The current move within the A l community toward capturing the semantic within the knowledge and creating knowledge models that can be shared and reused, has driven knowledge representation into a new era. The main approach for capturing and representing knowledge in this new framework is characterized by the use of ontologies. The term "ontology," which is now become extremely popular in the field of Artificial Intelligence, has its origin in philosophy. The historical meaning of the word ontology in philosophy is "the metaphysical study of the nature of being and existence" [WordNet]. This refers to a branch of philosophy called Epistemology, which deals with the nature and organization of the real world. The common understanding of this term in the A l communities is to the identification of the representable things that exist in a specific domain and the relationships amongst all of these existing things [Sowa 2000]. In other words, an ontology is a conceptual model, a resource containing knowledge about "concepts" that exist in the world and how they Chapter 2. Background and Related Work 13 relate to each other. A concept is a symbol for representing meaning with well defined attributes and relations with other concepts [Mahesh 1996]. In the following sections we discuss and describe the terms and concepts related to ontologies as well as provide the reason for using them as representational models for our history domain. 2.2.1 Why ontologies? There are several reasons to develop and use ontologies as a part of Knowledge Representation systems. The following is a list of reasons taken from ontology literature [Guarino 1997; Noy and McGuinness 2001]. • To clarify and share the structure of knowledge Many applications share common vocabulary and concepts. One of the main motivations for building ontologies is to enable sharing a common understanding of the structure of knowledge amongst people and applications. Different users or applications can use the same ontology to represent common terms and concepts in a particular domain of knowledge. These shared ontologies can later be used to facilitate knowledge extraction and manipulation from different systems, and reduce the high cost of knowledge acquisition. • To allow reusing knowledge The ability to integrate and reuse an existing ontology, without needing to rebuild it, provides a great benefit. One of the main motivations for ontology research comes from its capability to facilitate reuse of domain knowledge. There are two types of ontology reuse methods: merge and integration [Pinto, Perez et al. 1999]. o "Merge" refers to building an ontology in a domain reusing two or more different ontologies from the same domain. The ensuing ontology is a combination of the involved ontologies in a way that means one cannot identify the sources by having the resultant ontology (Figure 2-2). The purpose of merge is to create a Chapter 2. Background and Related Work 14 more general ontology by combining several other ontologies within the same domain. Figure 2-2 Merging different ontologies This figure illustrates what the resulting ontology of a merge process would look like. It can be seen that the resulting ontology (O) is a combination of the two involved ontologies (Ol, 02). However from the resulting ontology one can not identify which parts belongs to which original source. o Integration refers to building an ontology in a particular domain reusing ontologies from different domains. In an integration process, the involved ontologies remain largely unchanged, or at most undergo minor changes. It is possible to identify the sources by having the resulting ontology (Figure 2-3). An example of this can be seen in the reuse of an existing time ontology to create one that includes a time notion. Many models in different domains use the notion of time. A generic ontology for time can be included in developers' own models. In other words, i f an ontology has already been developed, it can be employed by other users in their models to capture certain aspects in their domains. Several existing ontologies can also be combined to build a larger ontology. Chapter 2. Background and Related Work 15 Figure 2-3 Integrating several ontologies into one more general ontology This figure shows how the source ontologies (O,, 02,03) in an integration process can be easily recognized in the resulting ontology Although reuse is referred to as one the biggest advantages of using ontologies in the literature, it is not clear how a merge or integration must be done. Ontology interoperability has been recognized as a challenging yet unachieved task. No current ontology building methodology really addresses this issue or deals with it explicitly. There is no consensus for the methods used in merging and integration. These are still unclear and more of an art than a methodology. These issues are still part of ongoing research in the area [Pinto, Perez et al. 1999; Beck and Pinto 2003]. Guarino [Guarino 1997] states that reusability can be acquired i f the domain knowledge has higher generality and granularity than the problem it intends to solve. Given that the knowledge is dependent on the problem it intends to solve, the main concern is how to relate the problem to the domain concepts. Different applications can make use of the same basic knowledge related to a domain, however, they need to adapt this knowledge base to solve their particular problems. We believe that, one cannot expect to find off-the-shelf ontologies and be able to use them to solve any given problem. However, we can Chapter 2. Background and Related Work 16 expect to find ontologies that can be easily modified to fit the needs of the desired application. • To make the assumptions used to create the domain explicit Making the domain assumption explicit helps with understanding, locating, and later altering these assumptions in case the knowledge about the domain changes. The description and meaning of the knowledge that has been captured in the ontology is explained and clarified in these assumptions. • To allow discerning between domain knowledge and the operational knowledge As described in the last section, ontologies can be classified into either domain or task ontologies. If the specification of the domain concepts is available, different types of tasks can be performed on the knowledge. On the other hand, the same task ontology can be applied to different domain ontologies using the same structure. • To study domain knowledge Having a formal specification of the domain knowledge helps with the study, reuse, and extension of an existing ontology. 2.2.2 Def in ing the term "onto logy" As mentioned before, the term ontology has its origins in philosophy. While within the philosophy community there is an agreement upon the definition of ontology as "a particular theory in metaphysics concerned with the nature and relations of being and the kind of existents", [Webster] there is some dispute amongst those in the A l community upon this term's meaning. Many definitions of ontology have been offered in A l literature; some of these contradict one another. This section gives an overview of the definitions of the term ontology within the A l community and follows with a definition that best suits the purpose of this research. To distinguish between the meanings of the term "ontology" in philosophy and A l , Guarino [Guarino and Giaretta 1995] delineates the following two terminologies: Chapter 2. Background and Related Work 17 • "Ontology" (with upper-case "o"), which refers to the philosophical meaning of the term, is "a branch of metaphysics which deals with the nature and organization of realty." • "ontology" (with lower-case "o") denotes the A l meaning of the term. People in different contexts and with different interests have proposed diverse definitions for the term. At a glance, an ontology represents some kind of world view with a set of concepts and relations amongst them, all of these defined with respect to the domain of interest. Some scholars redefine the term in an effort to capture an absolute view of the world. For instance, John F. Sowa [Sowa 2000a] defines an ontology as "The study of existence, of all kind of things (abstract and concrete) that make up the world" Uschold et al [Uschold and Gruninger 1996] describe an ontology as "A vocabulary of terms and some specification of their meaning" Given the vague nature of these definitions, it is unlikely that they will prove to be useful for those of us contemplating the creation of real usable ontologies. Having said this, there exists a set of more explicit definitions, which better capture the essence we are looking for. The most cited definition of the term is proposed by Gruber. In [Gruber 1995] Gruber defines the term as "An explicit formal specification of a conceptualization ". To clarify the definition, the following terminology has been proposed [Gruber 1995; Studer, Benjamins et al. 1998]. o "Conceptualization" is an abstract, simplified model of concepts in the world, usually limited to a particular domain of interest. o "Explicit" indicates that the type of domain concepts and the constraints imposed on their use are explicitly defined. Chapter 2. Background and Related Work 18 o "FormaF means that the ontology specification must be machine readable Taking into account that the main reason to create ontologies is knowledge sharing, Borst [Borst 1997] modifies Gruber's definition to "An ontology is a formal specification of a shared conceptualization " Studer et al. [Studer, Benjamins et al. 1998] combine the two definitions above, "An ontology is an explicit formal specification of a shared conceptualization " However, in [Guarino and Giaretta 1995] Guarino argues that an ontology is only a "partial account of conceptualization," not an explicit specification of conceptualization as Gruber claims. He identifies a conceptualization as a description for the intended meaning of the terms employed to represent the relevant relations. It has been argued that these meanings remain the same even i f they have been used in different contexts or arrangements. In other words, a conceptualization is a set of informal constraints imposed on the structure of the knowledge. As we can infer from what is stated above, the definition of ontology is closely connected to the interpretation of "conceptualization." Different interpretations of the term "conceptualization" produce confusion when interpreting the term "ontology." Researchers in different communities interpret the terms in a manner that better serves their purposes. This in turn gives rise to confusion and discrepancies that further complicate the clarification of these terms. In some definitions, conceptualization and ontology are kept clearly distinct. However, some others see the terms as indistinct. In either case, we can say that every ontology model for knowledge representation is either explicitly or implicitly committed to some conceptualization. The definition proposed by Guarino best serves the purpose of this thesis. We agree with Guarino that an ontology is, possibly, an incomplete agreement about a conceptualization and not a specification of the conceptualization. This means that an ontology is an agreement between people in a community sharing interest in a common domain. We reify the definition as Chapter 2. Background and Related Work "An ontology is an incomplete formal description of concepts and their relations in a domain of interest" 19 By "incomplete" we mean that the definition of concepts should be left open for further interpretation and manipulation by the users of the ontology according to their specific area and domain of interest and their intended application. "Formal" means that the ontology specification can be easily translated into a machine readable code, however, this is not mandatory when defining ontologies at an abstract level. We also believe that this definition must be left open to further interpretation regarding the specific area of interest and research and the application in which the ontology is used. 2.2.3 What do ontologies look like? An ontology is usually represented by concepts within a particular domain in a hierarchical form. This hierarchy can also be referred to as a taxonomy of the domain of discourse. Likewise, the concepts can be referred to as vocabulary or terms. The taxonomy is the central part of most ontologies. Almost any ontology includes something besides the taxonomy of concepts. A n ontology consists of concepts, relations amongst these concepts, and axioms which define constraints on these relations. These axioms are used to make the interpretation of the content (concepts and relations) within an ontology explicit (same across different systems). The relations and axioms associated with the concepts in an ontology form the "ontology content" which tries to capture the semantics of the domain. In contrast, a taxonomy represents the syntax of a domain. In short, for a taxonomy to be recognized as an ontology, it must have at least the following properties: [McGuinness 2002] • Finite yet extensible set of vocabulary • Unambiguous interpretation of concepts and their relationships • Strict hierarchical sub-concept relations between concepts Chapter 2. Background and Related Work 20 The taxonomy of an ontology can be a simple concept hierarchy or a complex hierarchy with dimensions at each level. An example of a simple taxonomy is a tree-like hierarchy representing concepts. The branches of this tree are "is-a" relations, and different branches growing from a concept to a sub-concept are disjoint. In a complex taxonomy, the general layout of the concepts is different. In this case, there are several top-level categories at the same level. These layers are subcategorized along parallel dimensions and described by combinations of values along these dimensions. As an example, a partial view of a simple newspaper ontology can be seen in Figure 2-4 through Figure 2-6. Figure 2-4 illustrates a partial view of the "is-a" (concept/sub-concept) relation within the newspaper ontology. From this figure we can say that a Salesperson is an Employee, and that an Employee is a Person. Figure 2-5 demonstrates the relations (other than the "is-a") that hold amongst the concepts. In this example, we can see that an Article has an Author. This Author can be a Columnist, a Reporter, an Editor, or a News-Service person. Subsequently, an Editor is responsible for Employees and so on. Figure 2-6 shows a constraint imposed on employee salary. This constraint states that no Employee can get a salary greater than the Editor who is responsible for him/her. Chapter 2. Background and Related Work 21 Person isa Author News Service Columnist Reporter Editor Salesperson Figure 2-4 Partial view of a simple newspaper ontology (concept/sub-concept relations) This figure illustrates the is-a (being type of) relation within the concepts in the ontology. We can see that a columnist is an author and an employee at the same time. Additionally, an employee is a type the more general concept person Advesiissmsni Stands isa \ rd_Ad Cohurmist Reporter Figure 2-5 Partial view of the newspaper ontology (relations amongst concepts) This figure illustrates the relations that hold amongst the concepts within the newspaper ontology. In this figure an editor, who belongs to a more general notion author, is at the same time responsible for employees who can be either columnists, reporters or salespeople. Chapter 2. Background and Related Work 22 ISllllIP^ leditor-employees-salary-constraint Sl.il<!:r.i:t£ 0 m 1% * ( f o r a l l ?editor ( f o r a l l ?employee (=> (and (respon3ible_for ?editor ?employee) (own-slot-not-null salary ?editor) (own-alot-not-null 3alary ?employee)) (> (salary ?editor) (salary ?employee))))) Dpsmptnin The salary of an editor should be greater than the salary of any employee which the editor is responsible for. !<<]>'lift! (defrange ?editor :FRAME Editor) (defrange ?employee :FRAME Employee responsible_for) Figure 2-6 Constraint imposed on concept property within the newspaper ontology (axiom) This figure shows a constraint imposed on the employee's salary. This constraint states that no employee can get a salary higher than the editor who is responsible for him/her. 2.2.4 Ontology classification There are different approaches for categorizing ontologies. The most common one classifies each ontology into one of the following four categories according to the specification and generality of the domain that it aims to represent [Guarino 1997; Noy and Hafner 1997; Beck and Pinto 2003]. • General or Top-Level ontologies Ontologies within this category are very general and aim to represent the various types of things that exist in the world without considering any particular domain or problem. The knowledge represented in this type of ontology includes terms related to general (top-level) concepts in the world such as things, events, processes, and spatio-temporal components. Because of their generality, these ontologies can be used across different domains. Some examples are represented in [CYC] and [Sowa 2000a]. The following Chapter 2. Background and Related Work 23 figures (Figure 2-7 and Figure 2-8) show upper level hierarchies in C Y C and Sowa's top-level ontology. Individual Object Intangible Event Process Intangible Stuff Represented Thing Relationship Figure 2-7 CYC ontology Part of CYC's Top-Level categories Independent Mediating Object;: Process Figure 2-8 Sowa's ontology Chart explaining the hierarchy of top-level categories in Sowa's ontology. This approach considers three distinct top-level categories: Concrete vs. abstract; Independent vs. Relative vs. Mediation; and Object vs. Process. John. F. Sowa categorizes concepts in the real world based on philosophical foundations. His approach has three distinct top-level categories as can be seen in Figure 2-8. o Concrete versus Abstract o Form (Firstness) versus Role(Secondness) versus Mediation(Thirdness) Chapter 2. Background and Related Work 24 These categories are not mutually exclusive. For instance, a Man is a Form since it can be described without considering anything exterior to a Person. In relation with other concepts the Man can take the role of a father, son, or teacher. Parenting is a Mediation since it relates several concepts to one another. o Object versus Process Objects maintain their identity over a period of time, whereas Processes change their state within a certain timeframe. • Domain-specific ontologies These ontologies represent knowledge specific to a particular domain of discourse. The Unified Medical Language System (UMLS) is an instance of a domain ontology (Figure 2-9). This system has been developed to assist retrieval and integration of biomedical information from several different sources. The main purpose of this project is to facilitate the use of different sources by people whose terminologies might be dissimilar. U M L S has both taxonomic and non-taxonomic hierarchies. The former are used to represent medical concepts and the latter represent the relations amongst these concepts [UMLS]. Another example of this type of ontology is the Toronto Virtual Enterprise (TOVE) project presented in [Fox 1992; Fox and Gruninger 1994; Gruninger and Fox 1995] (Figure 2-10). The project's goal is to create a generic, reusable enterprise model which is a computational representation of the structure, activities, processes, information, resources, people, behavior, goals, and constraints of a business, government, or other enterprise. Chapter 2. Background and Related Work 25 Entity Intellectual P roduc | Figure 2-9 UMLS Top-Level hierarchy of entities (adapted from [Noy and Hafner 1997]) Organization Entity Organization Individual Organization Group Board of Directors Division Department Figure 2-10 TOVE An Organization-Entity Hierarchy in the Organization ontology (adapted from [Noy and Hafner 19971) Since both top-level and domain ontologies try to represent knowledge about the real world, they share several key similarities which makes distinguishing between them Chapter 2. Background and Related Work 26 difficult. However, one should keep in mind that even when these two types of ontologies represent the same domain, their particular view of this domain can be different. • Application ontologies These kinds of ontologies contain both the domain and their related tasks. They not only express the concepts in a domain but also relate them to the tasks that can be performed on them. These ontologies are related to problem solving methods. They are used to describe the concepts employed to solve the problem associated with a particular task. As an example of this type of ontology, we present part of what is described in [vanHeijst, Schreiber et al. 1997]. This example uses CASNET [Weiss, Kulikowski et al. 1978] which allows the expression of causal links describing the processes associated with diseases and the development of diagnosis applications (Figure 2-11). Domain knowledge is represented in unlabeled boxes. Likewise, labeled boxes represent knowledge associated with problem solving methods. Causation Strength Casnet ranking \ ttreigtl Wi Casnet ranking Hue reel W ; Casnet ranking uelgtt Pathophysiological state Wf Casnet ranking FomuarrAwe Kg It Confidence , measure Casnet ranking ODifUeice EuUe tce-tbr Cost Casnet ranking com Observation 77** symptom Sign Lab-test History Figure 2-11 Example of application ontology Taken from [Beck and Pinto 2003] This figure presents a partial view of an application ontology in the medical diagnoses domain. This ontology not only allows expression of the domain knowledge (labeled boxes) but also the knowledge related to problem solving methods (unlabeled boxes). Chapter 2. Background and Related Work 27 • Representation ontologies or meta-ontologies These ontologies are specifically formalized in a manner that facilitates the sharing and reusing of knowledge. Developers and users alike employ them to share ontologies that utilize the same representation primitives to formalize knowledge. In meta-ontologies, the underlying conceptualization expresses the representation primitives. One example of this kind of ontology is the frame ontology presented by [Gruber 1993]. The frame ontology defines the terms that capture the conventions used in object-centered knowledge representation systems (Figure 2-12). It is created using the Knowledge Interchange Format (KIF), an ontology building language. Class RELATION Subclass-Of: Set Axioms: (<=> (Relation ?Relationl (And (Set?Relaton) (Forall f?Tuple)(=> (Member?Tupie 7Relation)(JJst?Tuple);!)I) Defined in theory: Frame-ontology Source cade: frame-ontology.lisp Also defined in: Kit-relations Class CLASS Subclass-Df: Relation Skits Of/hsianaes: Aritv: 1 Axioms: (<=> (Class ?Class) (And (R el atio n ?C lass) (Aritv ?Class) 1))) Defined in theory: Frame-ontology Source code: f ra rne-ontol ogy .I i sp Figure 2 - 1 2 Part of the frame ontology in Ontolingua (http://www.ksl.stanford.edu/software/ontolinguaA This figure represents two of the representation primitives that exist in the "Frame Ontology": "RELATION" which describes the association between concepts within an ontology, and "CLASS" which represents concepts in the domain that the ontology is intended to capture. When trying to better understand the above classification, one must take into consideration that people from different communities with diverse interests view the world from different angles. An important aspect in one context can be trivial or even insignificant in another. This leads us to believe that expecting to reach a universal consensus for a general ontology representing any part of the world with its concepts and relations in their entirety, is an unrealistic goal. Even i f this goal is achieved, it is still unfeasible to try to solve any particular problem with the obtained ontologies. Chapter 2. Background and Related Work 28 Likewise, domain-specific ontologies are not only empowered by but also limited by the particular applications that are intended to use them [Beck and Pinto 2003]. Even for the simplest case of a domain-specific ontology, there can be many different interpretations of the levels of importance and detail in the specification of concepts and relations. Notwithstanding, we believe that general ontologies should still be developed to serve as a resource and aid for. developing both domain and application ontologies. The key issue here is how to adapt a general ontology to build a domain-specific or application ontology. More importantly, integrating two or more ontologies, whether they are general or domain specific, remains an important issue. For general ontologies, the main concern is in the design, which should facilitate appending domain-specific ontologies to them. Similarly, for a domain specific ontology, the issue is whether it can easily reuse previously defined knowledge from a general ontology. Yet another issue is whether a domain specific ontology can be easily integrated into a more general one. 2.2.5 Methods for building an ontology-Building a well-developed, usable, and sharable ontology represents a significant challenge. There is great diversity in the way ontologies are designed as well as in the way they try to represent the world. Before ontology sharing and reuse become a practical reality, some standard should emerge to define what an ontology should consist of and how it should be represented. In short, we need to know how to build a usable ontology. A range of methods and techniques have been reported in the literature regarding ontology building methodologies. However, there is an ongoing argument amongst those in the ontology community about the best method to build them [Noy and Hafner 1997; Lopez and Perez 2002; Beck and Pinto 2003]. Most of the ontology building methodologies are inspired by the work done in the field of knowledge engineering to create methodologies for developing knowledge based systems (KBS). For example, the Enterprise Methodology (described in section 2.2.5.1), like most KBS development methodologies, distinguishes between the informal and formal Chapter 2. Background and Related Work 29 phases of ontology development. M E T H O N T O L O G Y (described in section 2.2.5.4) adapts the work done in the area of knowledge based evaluation for the ontology evaluation phase. A Knowledge Base (KB) is a knowledge model of a K B S . This K B contains both abstract and specific knowledge regarding a particular area defined in a computational format. There are similarities between knowledge bases and ontologies. Both K B and ontologies define, gather and represent knowledge about concepts and their relations in a computational format for a particular domain of interest. The additional feature provided by ontologies is the ability to reuse and share this knowledge. Ontologies prevent K B S developers from having to build K B ' s from scratch. Instead, they do so by using reusable components. However, knowledge bases and ontologies differ in the following characteristics [Perez 1994a; Perez 1994b]. First, the knowledge captured in ontologies is more general than that captured by KB ' s . Therefore, knowledge in ontologies is more appropriate for reuse and sharing across applications [Beck and Pinto 2003]. Second, ontologies differ from KBs in that they do not usually contain reasoning methods within themselves: Ontologies do not include methods relating them with the use of any kind of knowledge. Third, the language used to formalize K B ' s has an influence on the quality and quantity of the knowledge gathered in said KB ' s . However, the selected language to be used within an ontology has no effect on its knowledge [Perez 1994a; Perez 1994b]. Even though these two approaches, Knowledge Bases and Ontologies, differ in some aspects, they are still closely related and have a strong influence on each other. In the reminder of this section, we describe the most representative ontology building methods that address the problem of building ontologies from scratch. These are presented in chronological order. We analyze their approach, strong points, and shortcomings according to the following criteria: • Level of Detail and Clarity: how well is the methodology described? The approach is analyzed to determine i f it provides a precise and comprehensive description of the techniques and methods suggested. Chapter 2. Background and Related Work 30 • Techniques for Identifying Ontology Terminology Look at the techniques and strategies proposed for capturing the terms related to the ontology and how efficient these methods and techniques are. • Generality Determine whether the proposed approach is application dependent or not. There are two general points of view when it comes to building an ontology. The first considers building an ontology in general, the second concentrates on case studies in the development of a single ontology related to a particular problem or domain of discourse. None of the methodologies we analyze in this study are strictly case studies. However, each of them has a different degree of inherent generality. • Ontology Evaluation Analyze whether any techniques are provided to evaluate the completeness of the resulting ontology according to the specified requirements (if these were determined). • Usability Investigate whether the technique applies to building a real ontology. If this is the case, we study whether this ontology is successful according to the intended user community. We also determine i f the user community is closely involved in the development process. A l l of these methods and techniques are still determined to some extent by the particular circumstances in which they are applied. We must note that, in any given circumstance there might be no available guideline for deciding on what techniques and methods to apply [Uschold 1996]. 2.2.5.1 Uschold and King Methodology (Enterprise Methodology) The first methodology discussed here is originally proposed by Uschold and King [Uschold and King 1995] in 1995. They present a guideline derived from their own experience in building a particular ontology in an enterprise modeling process [Uschold, King et al. 1998]. Their goal is to introduce a comprehensive methodology (containing a set of techniques, methods, and guidelines) for building ontologies. Chapter 2. Background and Related Work 31 In this work, Uschold and King outline the stages they believe are required to build an ontology. Their approach is described in detail in this section. Their idea of a method for developing an ontology consists of the following four stages: • Identify the purpose and intended users • Building the ontology o Ontology capture o Ontology coding o Integrating existing ontologies • Evaluation • Documentation Figure 2-13 illustrates their approach. Identify concepts & relations Produce unambiguous definition Identify terms to refer to concepts and relations 1. Choose a representation language 2.. Write the code 1. How and Whether to reuse ontologies that already exists Figure 2-13 Uschold and King Methodology (Enterprise Methodology) This methodology is composed of four different stages: 1. Identifying purpose and users; 2. ontology building; 3. evaluation; and 4. documentation. As it can be noticed, the documentation takes place all along the development process. The following is a detailed description of each stage in the process: • Identify the purpose and intended users Chapter 2. Background and Related Work 32 It is important to know why an ontology is being developed and what purposes it must serve when it is complete. In other words, it is essential that ontology developers clarify their own purpose for building the ontology. In order to efficiently develop an ontology, the ontology creators must identify both the intended purpose and end users. According to Uschold, we can identify four major purposes for developing an ontology [Uschold 1996]: o Facilitating communication between people o Allowing interoperability amongst systems o Providing reusability o Knowledge acquisition • Building the ontology Uschold and King identify the following three main sub-steps in this section: o Ontology capture An important part of the effort involved in the development of ontologies is directed at identifying those categories and concepts in the real world that are of interest, defining them, and defining the appropriate terms to refer to them. This procedure is referred to as ontology capture in this methodology. The authors refer to ontology capture as an informal definition of the ontology. This stage consists of the following: a. Identification of the key concepts and relations amongst them in the domain of interest. (The main focus is on the concepts not the words used to represent them.) b. Clearly define such concepts and relations in a natural language text. c. Employ reference terms for these concepts and relations, d. Reach an agreement on all of the above. To determine the relevant concepts, a brain-storming session is used. However, according to them, there is a need for consulting with domain experts to avoid ambiguities and differences in opinion. This is followed by categorization of terms that are closely related into groups. The result of this process is a set of categories of terms. Chapter 2. Background and Related Work 33 An important issue in identifying and categorizing the concepts is deciding on the level of generality and granularity of the selected categories. In order to categorize the concepts, they adopt the middle-out approach proposed by Lakoff [Lakoff 1987]. The idea behind this approach is that the categories are not simply organized in a hierarchy from the most general to the most specific, but rather organized cognitively in a way that categories are situated in the middle of the general-to-specific hierarchy. Going up from this level is the generalization and going down is the specialization. In general, there are three approaches available for categorizing concepts in a domain of discourse: top-down, bottom-up, and middle-out. In the top-down approach, categorization starts from the most general concepts. The bottom-up approach first identifies the most specific concepts and then groups them into categories. In middle-out, categorization starts from neither the most general nor the most specific but from the most important concepts and evolves in both directions from there. The disadvantage of using the top-down approach is that since we start with a few general concepts we might suffer from ambiguity. On the other hand, in the bottom-up approach we may provide too much detail which might not be used in a final version of the ontology [Uschold and Gruninger 1996]. As stated before, Uschold and King employ the middle-out approach to construct the hierarchy of concepts in their case study. First, the most important concepts are identified and from there the rest of the hierarchy is captured through generalization (the top-down method) and specification (bottom-up). The next step in this phase is to identify the cross-references within and amongst the concepts in the groups. After constructing the categories, the next step in ontology capture is to provide an unambiguous definition for all the terms and decide i f they are important enough to be included in the ontology. Uschold and King provide a general guideline on how to produce definitions and how to handle the ambiguity in definitions as follows: a. Determine a precise and clear natural language text definition of all the terms, b. Dictionaries and other technical glossaries and most importantly, the domain experts are used to ensure the consistency of the newly added term with the terms already in use. c. Specify the relationship of the term being defined with other commonly used Chapter 2. Background and Related Work 34 terms that are similar to it. d. Provide additional information (and possibly examples) to help understand the meaning and usage of the term. The final step is to perform a critical review of the definitions. o Ontology coding According to the authors, coding is the explicit formal representation of the conceptualization acquired in the previous step (ontology capture). This includes choosing a representation language, and producing the formal ontology. o Integrating existing ontologies The authors do not present a clear definition of the subject but rather only note that the integration is a difficult problem to overcome which needs additional attention from the ontology community. The main issue is how to achieve an agreement among different users to be able to share and reuse an already defined ontology. • Evaluation The issue of evaluation is not clearly addressed by the authors. The approach taken is to adopt what has been done in the field of knowledge-based systems for evaluation and adapt it to ontologies. Competency questions [Gruninger and Fox 1994], the queries that the final ontology should be able to answer, are used to evaluate the ontology. However, unlike other approaches, they do not use competency questions to identify the concepts at the early stage of developing the ontology. They claim that competency questions are too specific to be used as a guide at this early stage. • Documentation Uschold and King suggest that important assumptions should be carefully documented. However, they do not provide a precise guideline on how this is to be done. Chapter 2. Background and Related Work 35 Analysis We refer to the previously proposed analysis criteria to present our opinion of Uschold and King's methodology: • Level of Detail and Clarity: how well is the methodology described? The authors outline the stages that should be taken when building an ontology but fail to provide enough detail for some of these steps. In particular the "Ontology Coding," "Integration" and "Evaluation" sections are only presented in a superfluous manner. • Approach to Identifying Ontology Terminology The main focus of this methodology is the ontology capture stage which includes identifying the ontology terminology. They focus particularly on categorizing and handling ambiguous terms. This work addresses this particular analysis criterion quite well, given its focus. The authors adapt common Knowledge Acquisitions techniques available at the time for defining this stage and also utilize the middle-out approach to categorize the ontological concepts. • Generality The proposed method is application-independent and very general. The procedure outlined in this work is completely independent of the intended application for the ontology. It can be used for developing a variety of different applications in different domains. • Ontology Evaluation The authors use competency questions to evaluate the completeness of the ontology but no detail is provided as to how this is done. The issue is addressed but not thoroughly. • Usability The authors apply their methodology to build an ontology called Enterprise Ontology [Enterprise]. The proposed ontology is a collection of terms and definitions relevant to business enterprises. This project is developed as a key element for supporting communications within the Enterprise Project and as a way to capture the knowledge related to enterprise domain. The Enterprise Project is a U K government promoted Chapter 2. Background and Related Work 36 project in enterprise modeling. The main goal of this project is to attain a wide view of an enterprise that can assist in decision making. According to the authors, the ontology is very general and contains most of the common terms relating to an enterprise. However, the application intended to use this ontology must modify or extend it to respond to any particular situation. The authors claim that the main part of the modifications deals with the extension of existing concepts toward more specialized terms to meet the requirement of the application purpose. The Enterprise Ontology consists of several conceptual components such as Activities and Processes, Organization, Strategy, and Marketing (Table 2-1) [Stader 1996; Uschold, King etal. 1998]. Activity Activity Specification, Execute, Executed Activity Specification, T-Begin, T-End, Pre-Conditions, Effect, Doer, Sub-Activity, Authority, Activity Owner, Event, Plan, Sub-Plan, Planning, Process Specification, Capability, ; Skill, Resource, Resource Allocation, Resource Substitute. Organization Person, Machine, Corporation, Partnership, Partner, Legal Entity, Organizational Unit, Manage, Delegate, Management Link, Legal Ownership, Non-Legal Ownership, Ownership, Owner, Asset, Stakeholder, j Employment Contract, Share, Share Holder. Strategy Purpose, Hold Purpose, Intended Purpose, Strategic Purpose, Objective, vision, Mission, Goal, Help Achieve, Strategy, Strategic Planning, Strategic 1 Action, Decision, Assumption, Critical Assumption, Non-Critical Assumption, Influence Factor, Critical Influence Factor, Non-Critical Influence Factor, Critical Success Factor, Risk. Marketing Sale, Potential Sale, For Sale, Sale Offer, Vendor, Actual Customer, Potential Customer, Customer, Reseller, Product, Asking Price, Sale Price, Market, Segmentation Variable, Market Segment, Market Research, Brand Image, Feature, Need, Market Need, Promotion, Competitor. Time Time Line, Time Interval, Time Point. Table 2-1 Enterprise Ontology Terminology This table illustrates the main conceptual components within the "Enterprise Ontology". These include Activity, Organization, Strategy, Marketing, and Time along with their related concepts. The Activity section is intended to capture any term related to performing an action within an enterprise. Two central concepts in the Organization section are Organizational-Unit and Legal-Entity. The former needs to be recognized only within the organization, Chapter 2. Background and Related Work : 37 however; the latter is also recognized outside the organization by legal authorities and has responsibilities and rights. A l l other terms in this section are defined around these two concepts. The Strategy section aims to capture all the terms related to the enterprise strategic plans, such as Purpose and Plan. Terms related to Marketing are categorized in the Marketing section. This section includes terms such as Sale, Sale-Price, Vendor, and so on. The authors state that the Enterprise project, and specifically, the showcased ontology is used in real cases by organizations promoting and involved in project development. For example, Lloyd's Register uses the results obtained from this project to allow for more effective modeling and re-engineering of business processes for strategic planning. I B M U K utilizes the results for modeling its own internal organization. However, we are unable to locate any detailed account of these implementations or any user feedback. The authors fail to report any evidence of taking into account usability issues in their development process. 2.2.5.2 Gruninger and Fox Methodology (TOVE Methodology) The second ontology building methodology to be reviewed is presented by Gruninger et al. in [Gruninger and Fox 1994; Gruninger and Fox 1995; Fox and Gruninger 1997; Fox and Gruninger 1998]. Gruninger and Fox define a method based on their experiment in developing an enterprise model called T O V E (TOronto Virtual Enterprise). They based their work on the ontology definition proposed by Gruber [Gruber 1993] "an ontology is a formal description of entities and their properties, relationships, constraints, and behaviors." In short, their approach can be described in the following stages [Figure 2-14]: defining motivations and requirements, identifying ontology terminology (informally and formally), defining constraints on the derived terminology, and finally, evaluation (examination of ontology completeness). Chapter 2. Background and Related Work 38 Motivating Scenarios "Informal Competency Questions Formal Terminology First-otcter logic identity possible problems and solutions Idenlty queries Idenfify concepts, relations, constraints Conditions under which the solutions to the queries are complete Defined as a first-order logic sentence using predicates of the ontology Completeness \ Theorems Formal Competency Questions Figure 2-14 Gruninger and Fox Methodology (TOVE Methodology) This figure illustrates the ontology development process in the "TOVE Methodology" proposed by Gruninger and Fox. The authors supplement their approach for guiding the design of ontologies with a framework to evaluate the adequacy of these ontologies. The steps proposed for this approach are explained here: • Identify Motivating Scenarios According to Gruninger et al., we need to develop a new ontology or extend an existing one when the existing ontologies do not address the problems in the applications. Gruninger and Fox define such problems as motivating scenarios. According to TOVE methodology, it is fundamental that any ontology development or extension proposal has a motivating scenario and a set of possible solutions for the problem stated in this scenario. An informal, natural, language text terminology of the concepts and relations in the ontology can be derived with the help of these scenarios. • Create Informal Competency Questions (Ontology Requirements) Based on the motivating scenarios acquired in the prior stage, a set of questions arises. These competency questions are the queries that the ontology must provide answers for Chapter 2. Background and Related Work 39 when completed. These questions justify the choice of concepts and relations in the ontology. At this stage, these questions are expressed in natural language text and are rather informal. Therefore, they are called informal competency questions. According to Gruninger and Fox, the competency questions should be organized and defined in hierarchical levels. This means that responses to lower level queries are required to also answer higher level (more general) queries. • Provide a Formal Ontology Specification Once the informal competency questions are in hand, the ontology terminology can be obtained from these questions. This terminology includes the concepts, their properties, and the relations amongst them. Gruninger and Fox opt for first-order logic to represent the terminology and competency questions in a formal language. Concepts, attributes, relations amongst them, and the constraints on them must be formally defined as well. The output of this phase is a specification for the definition of the terms and the constraints on them (definition). These are referred to as axioms. • Examine the Completeness of the Ontology According to Gruninger et al., by using the completeness theorem and a set of formal competency questions, we can evaluate the adequacy of the defined axioms for the ontologies by determining whether each and every competency question can be stated by a set of axioms defined for the terminology [Gruninger and Fox 1994]. Analysis • Level of Detail and clarity: how well is the methodology described? The primary focus of this work is on the formalization and evaluation phases. The approach does not explain other phases in depth, for example, it does not have any specific scoping phase. The authors do not address the issue of integration, even though the created ontology they describe is comprised of several separate ontologies. • Approach to identifying ontology terminology The authors propose to use motivation scenarios and competency questions for extracting the terminology, and adopt the middle-out approach for categorizing these terminologies. Chapter 2. Background and Related Work 40 However, neither of these methods is described in full detail. Furthermore, motivating scenarios are only one of several ways in which the tasks can be described. In order to obtain a more complete methodology, it becomes necessary to include other types of representation. • Generality Since the method uses competency questions and motivation scenarios, it is loosely application dependent. This is because these competency questions and motivation scenarios are dependant on the intended application. • Ontology evaluation Completeness theory is used to evaluate whether the ontology is able to answer all the competency questions. This theorem is based on whether the developers can formulate the competency questions, based on the defined axioms within the ontology. At the time (1995), the authors were the first to propose a formal evaluation of an ontology. The process consists of representing competency questions formally, and then by proving completeness theorems with respect to those questions based on the logical representation of concepts. This project makes an important step in an underdeveloped area of ontology research: formal representation and evaluation. • Usability According to the authors, the goal of the TOVE project [TOVE] is to introduce a generic, sharable and reusable computational representation of an enterprise model applicable across a variety of enterprises. To represent the knowledge within the enterprise an integration of the following ontologies is carried out (Figure 2-15) [Fox and Gruninger 1998]. Chapter 2. Background and Related Work 41 Figure 2-15 TOVE Ontologies (adapted from [Fox and Gruninger 1998]) • Activity ontology [Guarino and Pinto 1995] The activity ontology is developed to capture the actions performed within an enterprise, such as planning and scheduling. • Resource ontology [Fadel, Fox et al. 1994] The resource ontology is developed for use in manufacturing enterprises for modeling resources. Its aim is to enable applications to reason about the nature of resources and their availability. • Organization ontology [Fox, Barbuceanu et al. 1996] The focus of this ontology is on organization structure, roles, authority and empowerment. Figure 2-16 and Figure 2-17 illustrate the basic concepts of the organization ontology and part of the role hierarchy within the organization. Chapter 2. Background and Related Work 42 Figure 2-16 TOVE organization concept taxonomy (adapted from [Fox, Barbuceanu et al. 1996]) president Figure 2-17 Part of hierarchy of roles in organization ontology (TOVE) (adapted from [Fox, Barbuceanu et al. 1996]) • Quality Management Ontology [Kim, Fox et al. 1999] This ontology is developed to formally organize the body of knowledge regarding quality related concepts. The quality management ontology is used in conjunction with the ISO 9003 Micro-Theory in a lamp-making company to test the ISO 9003 compliance of the company. According to the authors, this ontology can be used later to develop Chapter 2. Background and Related Work 43 applications to reason about products, processes, or system-wide quality factors, so as to facilitate better quality management decisions. The authors of this methodology claim to have implemented a series of practical ontologies using this methodology. However, they fail to report any evidence of accounting for usability issues in their development process or their final ontologies. This leads us to conclude that the authors do not adequately address usability issues. 2.2.5.3 Uschold and Gruninger Methodology (Unified Methodology) In [Uschold 1996] and [Uschold and Gruninger 1996] Gruninger and Uschold merge the independently developed TOVE and Enterprise methodologies (discussed in the previous sections) and propose a new approach they call Unified Methodology. Both approaches emphasize separating the informal and formal stages in ontology development. One takes a formal view; the other, an informal view. These two approaches are different in the ontology capture and evaluation phases but are intended to be used in the same domain (enterprise domain). In this combined approach, the Enterprise Methodology [Uschold and King 1995] is used to capture the informal ontology with specific emphasis on issues such as scoping, handling ambiguity, reaching agreement and producing definitions. Likewise, the TOVE approach [Gruninger and Fox 1995] is applied to transform the previously obtained informal ontology into a formal ontology. 4 » * Informal evaluation Informal-"A \^ Onto logy ) /^FwmaT ^ S . /^PortrAi^N. (competencyy*— ( Concepis'&l) Create forma) ctefinitions and axioms , ' ' ' Formal evaluation Figure 2-18 Gruninger and Uschold Methodology (Unified approach) This figure shows the different approaches that can be taken with respect to the degree of ontology formality. Uschold and Gruninger take into account that the applicable methods for building an ontology vary with respect to the degree of ontology formality, its purpose, users, and the domain that it intends to capture. In short, they vary depending on the particular ontology being built. While building an ontology, one needs to decide on the level of formality desired. This is mainly determined by identifying the purpose and intended users of the ontology. The formality ranges from highly-informal (e.g. glossaries) through to structured but informal (e.g. the text version of Enterprise Ontology), semi-formal (e.g. formal version of Enterprise Ontology) to rigorously formal (e.g. TOVE). In general cases, the degree of formality required is proportional to the degree of automation in the tasks that the ontology is intended to support. The chosen method for building an ontology therefore depends on the degree of formality, which in turn depends on the intended purpose of the Chapter 2. Background and Related Work 45 ontology. For instance, for non-technical users, mainly domain experts, when the primary purpose is to build a shared vocabulary to facilitate communication between human users, an informal terminology glossary may be adequate. However, in order to allow inter-operability or reuse and sharing of knowledge, the ontology needs to be represented more formally. Some cases require that both formal and informal ontologies be built; this is in order to address the needs of both technical and non-technical users. In other cases it may still be useful to build a complete informal ontology, even when its intended users are technical. This ontology might be later used to document and define a formal encoding. Figure 2-18 illustrates the different approaches that can be taken in regard to the level of formality. The authors' goal is to provide a general and flexible guideline which can be applicable in different circumstances. Analysis The main concern with this work is the inclusion of both formal and informal approaches, and the provision of a comprehensive and unified guideline according to the level of formality that the ontology developer seeks. Even though this merging covers some of the shortcomings of previous methods, it still suffers from the same drawbacks we have mentioned before. Although this method now has more comprehensive capture, formalization, and evaluation phases, it still lacks a clear approach for integration and does not support general usability criteria. 2.2.5.4 Gomez and Fernandez Methodology (METHONTOLOGY) The last methodology to be analyzed is presented by Gomez-Perez et al. in [Perez, Lopez et al. 1996; Lopez, Perez et al. 1997; Blazquez, Lopez et al. 1998; Lopez, Perez et al. 1999; Lopez and Perez 2002]. According to Gomez-Perez et al., their goal for this work is to transfer ontology development from an art to an engineering discipline. The authors aim to define a standardization of the ontology life cycle (development) with respect to the requirements of the Software Development Process (IEEE 1074-1995 standard). This work has its origin in knowledge engineering methodologies for developing knowledge-based systems. The proposed methodology, " M E T H O N T O L O G Y framework" includes the clarification of the ontology development process, identifying a set of activities that Chapter 2. Background and Related Work ; 46 must be performed to build an ontology, an ontology life cycle that presents the order in which such activities must proceed, and presents techniques which can be used at each stage of the ontology life cycle. According to Gomez-Perez et al., all the activities that are carried out in an ontology development process may be classified into one of the following three categories: • Project management activities o Planning: identifying the main tasks to be carried out, their order, completion time, and the required resources (people, hardware, and software) o Control: assuring that the intended tasks fulfill the requirements they are designed for o Quality assurance: guaranteeing that the quality of each and every result (ontology, software, and documentation) of these processes is up to the required standards • Development oriented activities o Specification; identify the purpose and scope of the ontology. In the M E T H O N T O L O G Y framework, this includes: identifying the purpose of the ontology and its intended usage, scenario of use, users, level of formality of the proposed ontology and its scope (which contains its terminology, terminology's characteristics and granularity). o Conceptualization; organize the domain knowledge into a meaningful model at the knowledge level. o This work provides a guideline (set of tasks that must be performed) to organize the domain knowledge in a conceptual model (conceptualization). This conceptual model will describe the terminology of the domain of discourse, including concepts, their relations, structure, and inter-linked relations. The conceptualization guideline introduced in M E T H O N T O L O G Y provides a set of methods and techniques which not only assist the users in organizing the knowledge in a conceptual model but also helps users decide what to identify, Chapter 2. Background and Related Work 47 describe, formalize, and how to do it. Their approach for conceptualization is described in more detail in [Perez, Lopez et al. 1996]. o Formalization; representing the conceptual model as a formal model. This can be done with the use of description logic (logic-based) or frame-oriented (frame-based) representation systems. o Implementation of the ontology in a formal language: this means implementing formal models in a computational language. o Maintenance of the implemented ontology • Support activities o Knowledge Acquisition; obtain knowledge about a domain of discourse. They consider knowledge acquisition as an independent process in the development of an ontology. According to the authors, most of the acquisition is performed during the requirement specification stage and continues as the development procedure moves forward but to a lesser degree. The techniques that they propose for this stage include: a. Formal and Informal interviews with domain experts, b. Applying text analysis with the help of experts, books and handbooks, c. Using knowledge sources such as experts, books, handbooks, figures, tables and other ontologies, d. Integration; reuse existing ontologies when possible. This will involve finding the ontologies and testing whether the definitions to be borrowed are coherent with the terminology proposed in the conceptualization phase. o Evaluation; they define evaluation as "making a technical judgment of the ontologies, their associated software environment, and documentations with respect to a frame of reference." According to Gomez-Perez et al. evaluation should take place during each stage and between the stages throughout the ontology life cycle. o Documentation; to be able to use and reuse/share an ontology one must provide a detailed, clear, documentation for each and every step of the ontology development process. Chapter 2. Background and Related Work 48 o Configuration management; keep track of every version of documentation, software and ontology code to be able to track changes. The authors refer to the order of steps that should be taken to build an ontology as the "ontology life cycle." This life cycle closely resembles the classical software engineering life cycle (see Figure 2-19). M E T H O N T O L O G Y defines the following stages for the ontology life cycle: specification, conceptualization, integration, implementation, evaluation, and maintenance. Figure 2-19 illustrates that documentation, evaluation, knowledge acquisition, and integration are carried out through the entire life cycle of the ontology development. Earlier versions consider an integration stage between the formalization and implementation stages, but later versions consider this to be a support activity. For each and every phase of the ontology life cycle, certain documentation is produced. Planning Control Project management activities Quality assurance Development oriented activities Acquiring Knowledge Jntegratmg; £valuation> Documentations Figure 2-19 METHONTOLOGY ontology life cycle This figure illustrates the ontology development process according to the METHONTOLOGY framework. In this work, activities performed throughout the ontology development fall into one of three categories: project management, development oriented, and support activities. According to the authors, since the proposed model gives the user the flexibility to modify, insert, and delete concepts and relations to the ontology at any time, the ontology Chapter 2. Background and Related Work 49 life cycle is an evolving process. In an evolving prototyping life cycle, the developer can go back from any stage of the development process into any of the previous stages. As long as the ontology does not satisfy the specified requirements, this process can be repeated. Analysis • Level of Detail and Clarity: how well is the methodology described? Authors describe the steps that should be taken in depth and in a clear manner. The different techniques used are described in depth as well. However, the authors concentrate more on the conceptualization phases than the formalization and implementation stages. Therefore, their approach towards conceptualization is presented in a clearer more in depth manner. • Approach to identifying ontology terminology In this work, the authors adapt knowledge acquisition methods proposed in the knowledge engineering methodologies for developing Knowledge Based Systems. The proposed approach for categorizing terminologies is the middle-out approach. Within the conceptualization phase, very specific low-level steps are taken which can target domains where the intention is to capture terminologies, rather than functionality or behavior. In this case, the methods that they describe are well suited to these kind of domains. • Generality The general approach proposed is application independent. However, when it comes to the detail of certain conceptualization sub-steps, the techniques provided are somehow specific to the domain ontology they develope, and not applicable to other domains in a straightforward manner. • Ontology evaluation The authors adapted the "evolving prototype life cycle" for developing ontologies. Within the evolving prototype the evaluation takes place along the entire life cycle of the ontology. The evaluation is performed throughout each stage and between the stages all Chapter 2. Background and Related Work 50 along the ontology life cycle. They provide a set of guidelines to evaluate the completeness, consistency and redundancy of the created ontology [Perez 1994b]. This work is based on what has been done before in the area of Knowledge Based Systems evaluation. However, this process is not described in detail and rather a simple sketch of the general idea is provided. • Usability According to the authors, several ontologies in different domains built using the proposed method. One of these is the Chemical ontology, which consists of knowledge in the domain of chemical elements and crystalline structures [Lopez, Perez et al. 1999]. Figure 2-20 shows part of the planning and scope documentation for the Chemical ontology and Figure 2-21 illustrates the Chemical ontology concept classification tree. Domain: Chemical . /.<:'.•••:•.••/:<:'' • --v.; Date: May 15,1996 Developed by Asuncion Gdmez-Perez and Mariano Fernandez Lopez Purpose: Ontology about chemical substances to be used when information about chemical elements is required in teaching, manufacturing, analysis, and soon. Level at formality: SemrformaH. s . v ; Scc-pe: List at 103 elements: lithium, sodium, chlorine, mercury,,.... List of concepts: element, tjatogehfhotsfe gas, semlmctaJ. metal, thint-traitsi-tionmetal,.... tnfarmation about at least the tallowing properties: atomic: number, atomic might, electronegativity, melting point,.... Sources of knowledge: (a) Three Interviews with the expert. (b) The following books: IHandtaai, 84-S5] Handbook of Chemistry and Physics, 65th ed., CRC Pr*s$ Inc., 1984-19B5. Figure 2-20 Ontology requirements specification document for the Chemical ontology (adapted from [Lopez, Perez et al. 1999]) Chapter 2. Background and Related Work 51 Banaits Lanunides Figure 2-21 Part of the Chemical ontology (adapted from [Lopez, Perez et al. 1999]) According to Fernandez and Gomez, the Chemical ontology is being used in conjunction with several applications. One of these applications is an information-retrieval system that allows Spanish speaking users to consult and access, in their own language, the information contained in this Chemical ontology. The system uses this ontology in conjunction with a linguistic ontology to generate Spanish text descriptions as responses to the queries in the chemistry domain. Another application, which allows students to learn and test their skill in the domain of chemistry, uses Chemical ontology as the source of its knowledge. However, the authors do not mention how much the end-users are involved in the development process or whether their results are satisfactory to them. This leads us to conclude that the authors do not fully address usability issues. Analysis Summary Even though the methodologies presented here represent the state of the art as far as ontology building methodologies go, none of them has been standardized and established long enough to have a significant user community [Beck and Pinto 2003]. Therefore, a standard, universally accepted approach is yet to be defined. Chapter 2. Background and Related Work 52 Although there are some differences between the methodologies described above, most of these approaches include the following stages: specification, conceptualization, implementation, evaluation and integration. However, every methodology presented places emphasis on a different area or stage. There are three models to present an ontology life cycle: water fall, iterative, and evolving. Figure 2-22 illustrates how the stages go along each of these life cycle models. The evolving prototype gives the developer the flexibility to modify, insert, and delete definitions in the ontology at any time. The developer can go back from any stage of the development process into any of the previous stages. As long as the ontology does not satisfy the specified requirements, this process can be repeated [Beck and Pinto 2003]. An iterative life cycle consists of several complete iterations or prototypes of an ontology to be developed. The water-fall approach tries to attain the final ontology in a single attempt with a sequential progression through the life cycle. life cycle —| A i [»[" A2 [ » | AJ. "[— final product Waterfall Iterarive Evolving Figure 2-22 Water-fall, iterative, and evolving approach (adapted from [Beck and Pinto 2003]) The methodologies described in this section use either water-fall life cycle models (TOVE and ENTERPRISE) or the evolving prototype life cycle (METHONTOLOGY). When developing a small ontology with clear precise requirements, a water fall approach may be sufficient, whereas when it comes to building large ontologies with evolving requirements to begin with, the evolving prototype life cycle may be more appropriate. In real world scenarios, it is rarely the case that the requirements are clearly defined at the Chapter 2. Background and Related Work 53 outset. It is for this reason that an evolving prototyping life cycle may be more reasonable to use rather than a waterfall or an iterative model. None of the described methodologies addresses the issue of usability. In some part, this is due to the fact that for most of the ontologies that have been developed, the users and developers are the same people. In other words, ontologies are built to be used within the developer's institution and little to no regard to traditional usability issues was given. Another probable reason for the lack of usability studies in the presented ontologies is the innovative aspect that these ontologies still carry. For the most part, the researchers have focused on the ontology building methodologies as their main research goal. This in turn leads to work that is sometimes truncated beyond the implementation phases. The studies presented here are still in a stage where the main focus is on a research and experimental level and therefore little concern for usability is given in these reports. From what is reported in the studies, it appears that an engineering group was appointed to collect and analyze the requirements from the users and later delivered a final version without further consultation from them. As a final word, we should note that there is no one exact method to build an ontology. One can always find feasible alternative ways. The most appropriate techniques almost always depend on the characteristics of the domain the ontology is intended to capture and the to-be-developed application(s) [Noy and McGuinness 2001]. We believe that a comprehensive methodology should present guidelines to aid ontology developers to select amongst the available methods, according to the given circumstances. Chapter 3. Methodology 54 3 Methodology As discussed in the previous chapter, it is quite clear that building ontologies is still a matter of craft rather than a well defined engineering process. To this day, there is no agreed upon standard methodology for building ontologies. For our intended purposes, we have adapted different methodologies for the different steps in the ontology development process. This chapter begins by presenting the steps taken to building our ontology and the adopted techniques used for each step. The first step is a general explanation of how knowledge acquisition is carried out throughout the process. This is followed by a description of our conceptual ontology creation process. Later, we present the formalization and instantiation of the conceptual ontology by utilizing a tool called Protege. This tool was selected from several available, due to characteristics described in this chapter. A comparison of the available tools is presented in this chapter as well. 3.1 Selected Approach In our opinion, the ontology building process can be divided into the following stages: • Identifying the purpose, scope, and users • Ontology Building o Domain analysis and knowledge acquisition o Integration of existing ontologies o Building a conceptual (informal) ontology model o Transferring the conceptual (informal) ontology into a formal (machine readable) ontology • Ontology evaluation For our implementation, we have chosen an evolving prototype for ontology development. In this model, every step forms part of an evolving process. Each stage can have more than one iteration. At each stage, it is possible to go back to any previous stage of the development process, in order to satisfy emerging requirements. This makes the evolving prototype useful for developing any ontology from scratch. Figure 3-1 Chapter 3. Methodology illustrates how these steps are related, and in what order they can be performed to complete the ontology building process. 55 Evaluating ] Identify purpose, scope,and intended users Analyzing Domain Building conceptual ontology I Building formal : orlolooy- , i O o o c 3 £ o 3 3 O a (Q > o A C « o 3 3 a> (Q 1 o 3 Figure 3-1 Our Ontology Development process This diagram explains the steps taken to build our ontology. We used an evolving prototype to build our ontology. Integration, Knowledge Acquisition, and Documentation are carried out throughout the entire development process. We consider the following ontology design criteria for each and every stage of the development process [Gruber 1995; Swartout, Patil et al. 1996]. • Clarity: An ontology should provide a precise definition of terms. The terms should make sense to their intended users and not seem arbitrary or ambiguous. The definition must be objective and independent of context. Where possible, definitions should be complete, and not partial. Additionally, every definition should be documented using natural language. • Coherence: An ontology should be coherent. This means that it should allow making consistent inferences of definitions. For example, i f a sentence that can be inferred from the axioms contradicts a definition or example given informally, then the ontology is incoherent. Chapter 3. Methodology 56 • Extensibility: A n ontology should be designed to support revision and extensions. It should offer a conceptual foundation for a range of anticipated tasks. Also, it should allow inclusion of new terms (both for generalization and specialization) based on the existing vocabulary without requiring revision of the existing definitions. • Minimal encoding bias: An ontology's conceptualization should be specified at the knowledge level and be independent of any particular representation language. Minimal encoding bias enables knowledge-sharing and ontology reusing amongst different applications, which might use different representation languages. • Minimal ontological commitment: An ontology should make as few claims as possible about the world being modeled; this allows the involved developers liberty to specialize and instantiate the ontology as necessary. These claims, called ontological commitments, facilitate intended knowledge sharing activities. One way to minimize the ontological commitment is to define only those terms that are essential to the communication of knowledge. These criteria often present conflicting interests. We have considered this while developing our ontology and tried to maintain a balance between all the criteria presented here. 3.1.1 Identify the purpose, scope, and intended users In this stage of the ontology development, the purpose, scope and intended users of the ontology are identified. In order to do so, we provide answers to the following list of questions: 1. For what purposes is the ontology being developed? (Purpose) 2. What is the domain that the ontology will cover? (Scope) 3. What types of questions must the information in the ontology answer? (Purpose and Scope) 4. Who will use the ontology? (identify and characterize the range of intended users) 5. What is the level of formality required for the ontology? (Scope) Chapter 3. Methodology 57 The result of this phase is a set of answers to the stated questions, or in other words, "the requirement specification document." Our approach answers the selected questions in a manner similar to that proposed by Uschold and Gruninger [Uschold and Gruninger 1996]. In order to answer question 1 (For what purposes is the ontology being developed?), we provide a list of activities that the ontology is intended to support. The following is a list of purposes for building Ontologies taken from literature on the subject [Uschold 1996; Noy and McGuinness 2001]: • Facilitating communication between people * • Allowing interoperability amongst systems • Providing Reusability * • Knowledge Acquisition * The selected set of purposes to be supported by our ontology are explained in section 4.1. Question 2 (What is the domain that the ontology will cover?) and question 4 (Who will use the ontology?) relate to the scope and intended users of the ontology. By scope we mean the domain that the ontology will cover. This includes identifying the granularity and generality of this domain. This is further investigated in the next stage of development when the domain analysis and knowledge acquisition are done. In order to answer question 3 (What types of questions must the information in the ontology answer?) we identify fairly general motivating scenarios and competency questions and use these to help clarify specific applications and activities to be supported by the ontology. We use a set of motivating scenarios to define the problems that the ontology addresses and investigate possible solutions for these problems [Gruninger and Fox 1995]. This is followed by creating a set of informal competency question that we expect the ontology to be able to answer. At this stage, these questions are fairly general and do not introduce all the aspects or concepts of the ontology. Later, these motivating scenarios and competency questions can be used to extract the concepts, terms and semantic of the ontology [Uschold and Gruninger 1996]. For our Chapter 3. Methodology 58 ontology, these scenarios and questions are obtained from books in the history domain, brainstorming sessions, informal analysis of our text and inspecting available applications with similar purposes [Lopez, Perez et al. 1997]. The fifth and final question that we need to provide an answer for is "What is the level offormality required for the ontology?" Our approach has both informal and formal representations at different stages of development. First, we develop an informal model, which is later transformed into a formal representation, by using an ontology development tool. 3.1.2 Ontology Building Some research has been done towards automatically extracting ontological knowledge from natural language text. The main purpose of these studies is to reduce the manual effort involved in building ontologies [Alani, K im et al. 2003]. Up to now, most ontologies have been built manually. We use a manual approach since automatic extraction is still under development. This step in the ontology development process concentrates on domain analysis and knowledge acquisition, and building conceptual and formal models of the ontology. These processes are further explained in the following sections. 3.1.2.1 Domain analysis and knowledge acquisition The output of this phase is a set of concepts and terms covering the full range of information that the ontology must characterize to satisfy the requirements identified previously. In this phase, we use a glossary to gather the set of terms that must be included in the ontology [Lopez, Perez et al. 1997]. We use knowledge acquisition techniques such as brainstorming, in conjunction with informal analysis of the text to gather all potential relevant terms into a glossary of terms [Blazquez, Lopez et al. 1998]. The informal analysis of the text is carried out by providing more in-depth motivating scenarios and expanding the number and refining the granularity level of the competency questions. Within these brainstorming sessions, no term is excluded. Therefore, we must have some way to trim the set of terms down to a desirable and manageable size. There are two main reasons for removing a term: lack of relevance or duplication [Uschold and King 1995]. Chapter 3. Methodology 59 The result of these sessions is an informal natural language text terminology. Since our model is an evolving process, in the first attempt, we extract a comprehensive list of terms without worrying about overlap between the concepts they represent, relations amongst the terms, or any properties that the concepts may have. At later iterations, this list can be modified. In addition to identifying the set of terms, we also produce informal definitions for these terms. The procedure through which we obtain these definitions helps us address the problem of handling irrelevant, ambiguous or duplicated terms. We also have to make sure that all terms and the provided definitions for them purvey the desired meaning in the intended domain. The level of detail provided by these definitions must be consistent. In order to do this we use the following guideline [Uschold 1996]: • Develop natural language text definitions, being as precise as possible. • Maintain consistency with terms already in use, in particular: o make use of dictionaries and other technical glossaries o avoid introducing new terms where possible • Indicate relationships with other terms similar to the ones being defined. • Avoid circular references. • Provide any additional information that may help in understanding the definition. • Give examples where appropriate. It is important to remember that Knowledge Acquisition is an activity which is carried out iteratively throughout the ontology development process [Lopez, Perez et al. 1997]. 3.1.2.2 Investigate the possibility of using an existing ontology Throughout the ontology building stages, we query existing libraries of ontologies, such as Ontolingua [Ontolingua], D A M L [DAML], and the SUMO [SUMO] ontology libraries to search for similar or related ontologies which might be useful for us. The idea behind this is to look for relevant ontologies that can be integrated with our own ontology in order to speed up the development process as well as to gain a better insight of how to Chapter 3. Methodology 60 build a particular area or set of concepts within our ontology. We also survey the ontology literature for relevant work in this area. 3.1.2.3 Building an informal ontology model In this phase we structure the domain knowledge into a conceptual model. This means that the terms obtained from the previous step get organized and their correlations explained. This stage can be sub-divided into the following activities: • At this stage we expand our glossary of terms contains all concepts, relations, their definition or meaning, and additional information such as examples to clarify the meaning where appropriate. This terminology represents the knowledge we intend to capture with our ontology forms our glossary of terms. The output of this stage evolves as the ontology development activity proceeds. Table 4-7 shows a part of the glossary of terms obtained during of our development process. • Once we have a relatively complete glossary of terms, we identify concepts, relations within the concepts, and their attributes. We use the guideline provided in [Noy and McGuinness 2001] to do so. A short description of the guideline in presented here: o To define the concepts, we select the terms that express things having an independent existence rather than terms that describe these things. These terms are the concepts in our ontology and become anchors in the concept hierarchy. o After selecting all the concepts from the glossary of terms most of the remaining terms are likely to be properties of these concepts. For each property we must decide which concept it describes. These properties either specify an attribute of a concept or its relation with other concepts. o Attributes for these concepts can be identified by using motivating scenarios and competency questions in conjunction with the glossary of terms. These attributes define the internal structure and characteristics of the concepts. o The relations are mostly the verbs in the competency questions and motivating scenarios. These terms represent the associations that hold amongst the concepts in a domain. Chapter 3. Methodology ' 61 The results are stored in document tables called the Concept Dictionaries [Blazquez, Lopez et al. 1998]. Table 4-8 illustrates a part of one of our concept dictionaries. At this stage, the concepts are structured into naturally occurring groups. For example, concepts most related to one another are placed within the same Concept dictionary. This helps us build a conceptual graph of the ontology where we can visualize these relations and groups. • For the next step, we use the previously generated concept dictionaries and a middle-out approach to develop our graphical conceptual ontology model. The middle-out approach operates by identifying the most important concepts first and then generalizing or specializing these concepts within the group from that point. This approach was chosen amongst the other available approaches, since the concepts "in the middle" tend to be the more descriptive concepts in the domain [Noy and McGuinness 2001].Our conceptual model not only represents the concept hierarchy taxonomy but also the other (other than taxonomic) relations that hold amongst the concepts within our domain. A taxonomic relation can be interpreted as a "is-a" or "kind-of' relation. We organize the concepts into a hierarchical taxonomy by looking at cases where an instance of one concept is an instance of some other more general concepts. In other words, i f a concept A is a super-concept of concept B, then every instance of B is also an instance of A. This means the class B represents a concept that is "kind-of or a "type-of' A. Additionally, all sub-concepts of a concept inherit the properties of that concept. We adapt a simple Entity Model (ER) to illustrate the concepts and relations amongst them at this stage. We call this graphical representation of concepts and relationships "the conceptual ontology." Figure 4-6 illustrates a part of our conceptual ontology. 3.1.2.4 Building a formal ontology model The next step in our approach is to build a formal ontology based on the conceptual model developed in the previous section. In order to do this we utilize an ontology development environment. We analyzed several well-known available ontology development tools to choose the one that best suits our purpose and selected criteria. A Chapter 3. Methodology 62 comparison of these tools and the criteria used to select amongst them is presented in this section as well. 3.1.2.4.1 Selecting a development tool A large number of ontology development tools are available nowadays. In order to select the most appropriate tool, it is necessary to evaluate these tools against a set of criteria important to the user. Some studies have been conducted to evaluate ontology development environments previously, those presented in [Duineveld, Stoter et al. 2000] and [WebOnto 2002] are the most comprehensive ones. In [Duineveld, Stoter et al. 2000] a comparative study of several ontology development tools is presented based on a proposed evaluation framework. This evaluation, called the WondetTools project, was the earliest systematic survey which evaluated and compared the ontology building tools. In [WebOnto 2002] a comprehensive and general study of ontology-based environments is presented. This survey intends to cover tools which support activities such as creating, integration, evaluation, and storage and querying. An evaluation framework for each type of tool is proposed. Eleven different ontology-based tools were compared against their corresponding framework. These studies define an extensive set of criteria to be used for evaluating these tools. Some of the aspects that this framework compared include the following: • The ability to interact with other tools and to import and export ontologies in different formats; • the expressiveness of the knowledge model; • ' scalability and extensibility; • usability. Table 3-1 to Table 3-6 and Figure 3-2 show the results of the comparison and analysis. Chapter 3. Methodology 63 Feature Developers Availability Extensibility Ontology Storage Apollo K M I (Open University) Open Source Plug-ins Files LinkFactory Language & Computing nv License on site or ASP Yes D B M S OILEd University of Manchester Open Source No File OntoEdit Free Ontoprise Fre eware Plug-ins File OntoEdit Professional Ontoprise Software license Plug- ins File D B M S Ontolingua K S L (Stanford University) Free Web access None Files Ontosarus ISI (University of Southern California) Open source and free Web access to evaluation version None Files OpenKnoME University of Manchester Freeware None File Protege-2000 SMI (Stanford University) Open Source Plug-ins File D B M S (JDBC) X M L SymOntoX L E K S (IASI CNR) Free Web access No X M L W E b O D E Ontology Group (UPM) Software license and free Web access Plug-ins D B M S (JDBC) WebOnto K M I (Open University) Free Web access No File Table 3-1 a general description and design features of the tools within the Onto Web framework (based on the work in [WebOnto 2002]) Feature Graphical Graphical prunes Zooms Collaborative Ontologies taxonomy (views) working libraries Apollo Yes Yes No No Yes LtnkFactory Yes Yes Yes Yes Yes OILEd No No No N D Yes OntoEdit No No No No No Free OntoEdit No No No Yes Yes Professional Ontolingua Yes No No Yes Yes Ontosarus No No No Yes No OpenKnoME No No No Yes Yes Protege-2000 Yes Yes Yes Yes Yes SymOntoX Yes Yes No Yes Yes WEbODE Yes Yes No Yes No WebOnto yes Yes No Yes yes Table 3-2 Usability features supported (WebOnto framework) This table presents the different usability aspects supported by the different available ontology building tools, (adapted from [WebOnto 2002]) Chapter 3. Methodology 64 Feature Built-in inference engine Other attached inference engine Constraint / Consistency checking Apollo No No Yes LinkFactory Yes Yes (frozen ontologies) Yes OILEd Yes (FaCT) No Yes OntoEdit Free No No Yes OntoEdit Professional Yes (OntoBrocker) No Yes Ontolingua No Yes (ATP) No Ontosarus Yes Yes Yes OpenKnoME Yes No Yes Frotege-2D00 Yes (PAL) Yes Jess FaCT Flogic Yes SymOntoX Yes No Yes WEbODE Yes (Prolog) Yes (Jess) Yes WebOnto Yes No Yes Table 3-3 Inference services provided by the tools (WebOnto framework) (adapted from [WebOnto 2002]) Chapter 3. Methodology 65 Feature Intexoperabuiry with other ontology took Iny oris from languages Exports io languages KR paradigm of knowledge model Axiom language Methodology support Apollo No Apollo meta-language OCML CLOS Frames (OKBC) Unrestricted No LinkFactory FastCode TeSSI X M L RDF(S) DAML+OIL XML,RDF(S) DAML+OIL HTML Frames + FOL Proprietary Yes OILEd FaCT RDF(S) OIL DAML+OIL OIL, RDF(S) DAML+OIL SHIQ dotty HTML DL (DAML + OIL) Yes (DAML + OIL) No OntoEdit Free OntoAnnotate Ontobraker OntoiVkt Semantic Miner X M L RDF(S) FLogic DAML+OIL X M L RDF(S) FLogic DAML+OIL Frames + FOL Yes (FLOGIC) Yes (Onto-Knowledge) OntoEdit Professional OntoAnnQtate Ontobroker QntoMat Semantic Miner X M L RDF(S) FLogic DAML+OIL X M L , RDF(S) FLogic DAML+OIL SQL-3 Frames + FOL Yes (FLCGTC) Yes (Onto-Knowledge) Ontolingua Chimaera CML Model Fragment Editor Equation Solver Data structures inspector Expressions Evaluatar CKBC Ontolingua IDL KIF KIF, CLIPS CLIPS sentential format CML ATP EpdKit, IDL KSLruls engine LOOM OKBC syntax PROLOG systax Frames + FOL (Ontolingua) Yes (KIF) No Ontosarus LOOM, IDL ONTO, KIF C++ LOOM IDL ONTO, KIF C++ DL (LOOM) Yes (LOOM) No QpenKnoME GCE(GALEN CASE Environment) SPET GRAIL GALEN IR GRAIL, CLIPS HTML GALEN IR DL (GRAIL) Yes (GRAIL) Yes (GALEN) Protege 2000 PROMPT OKBC JESS FaCT XML, RDF(S) X M L schema OWL XML, RDF(S) X M L schema Flogics, CLIPS Java, HTML OWL Frames + FOL + Me tac lasses Yes (PAL) No SymOntoX -- -- OPAL OPAL Yes (OPAL) WEbODE JESS, PICSEL OILEd ODEMeige ODE-KM X M L RDF(S) CARIN Frames + FOL Yes (WAB) Yes (MethontalDgy) WebOnto PlarctOnto Sc holOnto OCML Frames + FOL Yes (OCML) No Table 3-4 Interoperability, knowledge representation, and methodological support comparison (adapted from [WebOnto 2002]) Chapter 3. Methodology 66 1. General 1. Evaluate the clarity of the interface 2. Evaluate the consistency of the interface 3. Evaluate the speed of updating after new data is inserted 4. Is there a good overview of the ontology? 5. Is the meaning of the commands clear? 6". Are the changes identifiable by a certain command clear to the user? 7. Evaluate the stability of the tool (crashes, etc.) 8. Does the tool require a local installation? 9. Evaluate the help-system 2 . Ontology 1. Is it possible to use multiple-inheritance? 2. Is it possible to create exhaustive and/or disjoint decomposition? (+ease of doing this) 3.1 Does the tool check new data for consistency with the ontology? 3.2 A t what level? (types, disjointness, etc.) 4. Are there example-ontologies available in the tool? 5. Does the tool provide libraries of ontologies that can be re-used? Through what operation? (inclusion, union, etc.) 6. Are there high-level primitives? 7. Is there information about the terms used in constructing an ontology in the help-system? 3. Cooperation 1. Does the tool allow synchronous editing of the same ontology by different users? 2. Are there ways to lock the ontology? 3. Is it possible to browse an ontology if it is locked? 4. Are the changes made by other users easy to recognize? 5. Is it possible to export the ontology's code in various formats? 6. Is it possible to import an ontology-description from another tool? Table 3-5Evaluation framework of the WonderTools Project (adapted from [Duineveld, Stoter et al. 2000]) • Pre-knowledge needed of underlying knowledge representation language • Difficulty of learning Ontolingua WebOnto ProtegeWin Ontosaurus ODE Figure 3-2 Results for ease of use comparison of the selected tools (WonderTools project) (adapted from [Duineveld, Stoter et al. 20001) Chapter 3. Methodology 67 Criteria Ontolingua WebOnto Protege Win Onto Saunas ODE 1. General 1.1 interface clarity + + -1.2 interface consistency + + + + + 1.3 speed D£ updating - 0 + - + 1.4 overview Q + + • 1.5 meaning of commands + + + + 0 1.6 identiflability of changes Q 0 0 0 0 1.7 stability + + + + -1.8 local installation No No Yes Yes/no Yes 1.9 help-system + - + + 2 . Ontology 2.1 multiple inheritance Yes Yes Yes Yes Yes 2.2 decomposition types + + + + 2.3.1 consistency checking + + + + + 2.3.2 level of checking 0 0 + 2.4 example ontologies + + 0 + 0 2.5 reusable ontologies + + + 2.6 high-level primitives + + + + 2.7 ontological help - - + 3. Cooperation 3.1 synchronous editing + + + » 3.2 ontology locking + + - + • -3.3 browsing when locked + + N A + N A 3.4 change recognition 1 1 |»y - - . . 3.5 export facilities + - - + 0 3.6 import facilities + - - + + Table 3-6 Summary of the results obtained in the WonderTools Project (adapted from [Duineveld, Stoter et al. 2000]) In this chart, a plus sign (+) means a positive result for the feature specified. In a similar manner, a zero (0) means a reasonable result, a minus (-) represents a negative result, and 'NA' stands for not applicable. We should consider that these results are based on a study carried out in 1999 and since then many of these tools have evolved. As an example of this, the later version of protege-win, protege-2000, supports cooperation and has import and export facilities. The results gained from these evaluations helped us narrow down our list of candidates to: Ontolingua [Ontolingua], OntoEdit [OntoEdit], WebODE [WebODE], and Protege-2000 [Protege]. We followed this evaluation by developing a very simple ontology using these four environments. We eventually decided to use Protege-2000 for the following reasons: • Availability • Ease of learning Chapter 3. Methodology 68 • Flexibility • Customizability • Large and active user community • Help availability (mailing lists, e-mail, FAQ, manual, annual workshops) • Possibility of importing and exporting ontologies in different formats The following section gives a short overview of Protege-2000. 3.1.2.4.2 Protege-2000 Protege-2000 is the latest generation of the Protege toolset. It was developed at Stanford University to facilitate knowledge acquisition activities [Grosso, Eriksson et al. 1999]. Protege-2000 is an extensible, platform-independent environment for developing and editing ontologies and knowledge bases [Noy, Fergerson et al. 2000; Noy, Sintek et al. 2001]. Protege was originally developed 16 years ago to support knowledge acquisition for a rather specialized medical expert systems. It has gradually gained popularity and now is used for many other purposes in different fields [Gennari, Musen et al. 2003]. It currently has more than 12,000 registered users all around the world [Protege]. Protege is open source and freely available for download under the Mozilla open source license. There are several features that make Protege stand out amongst ontology development environments [Protege FAQ]: • Intuitive and easy-to-use graphical user interface Protege-2000 provides a highly usable graphical and interactive user interface for the ontology development process. It allows ontology developers and domain experts to perform knowledge-management tasks such as creating and modifying reusable domain ontologies, customizing knowledge acquisition forms, and entering domain knowledge [Noy, Sintek etal. 2001]. • Scalability Protege-2000 uses a database as back-end and a cache mechanism to support the development of ontologies. This facilitates creation of large scale ontologies without suffering from performance loss as the ontology grows larger. There are examples of ontologies built using Protege-2000 with 150,000 elements. Chapter 3. Methodology 69 • Extensible plug-in architecture One of the major advantages of the Protege-2000 architecture is its modular, open construction. Protege-2000 can be easily extended using plug-ins created to perform specific user-required tasks. This plug-in architecture allows developers to add customized components to provide new functionality. Plug-ins can be classified in the following categories[Grosso, Eriksson et al. 1999; Knublauch 2003]: o Small user-interface components, called slot widgets, are designed to suit specific display or input requirements for a particular domain (Table 3-7). o Custom back-end plug-ins, called storage back-end, allow users to import, export, and store ontologies in different formats (Table 3-8). o Tab Plug-ins, called tab widgets, allow the inclusion of external applications to be used with Protege-2000. An example of this is an application that presents a visualization of the ontology components (Table 3-9). The Protege Plug-in Library has a collection of contributions from developers all over the world. Table 3-7, Table 3-8, and Table 3-9 show a list of the available plug-ins and a brief description for each of them. Chapter 3. Methodology 70 Slot Widgets Developer Description Bayesian Network Rafael Penaloza Make approximate inferences over ontologies where classes are arranged in " D A G " form Calendar K M center Provides date entry via a calendar Date fMRI Da ta Center Provides flexible date entry Date Fullbeing Hu Generates the current date and t ime in a predefined format Date Phillip Cheng Automatical ly fills in a s lot value wi th current date and t ime Display GIF Image ICS (university of California Display GIF images from the file system in Protege forms it) Display Indirect Instances Emotional Brain Automatical ly displays all the indirect instances of a class Get Author Stanford University Automatical ly fills in a s lot value wi th a user name J ava Function C alls Slot Widgets and Storage Backend Ifgi University of Munster A group of plug-ins that allows the description of things in flux, activit ies, and processes which cause a knowledge base to change over a t ime scale Measurement fMRI Da ta Center Provides flexible measurement entry Media University of South Hampton Include and display video and audio files Numeric Inference Engine PCM Center Performs simple numeric inferences such as unit conversion and multipl icat ion P ower-plant C ontrol Henrik Erikson Edit control rules for a simple nuclear power plant s imulator Swap Values Stanford University Swap slot values between slots Table 3-7 Slot widgets in Protege-2000 This table presents a sample of the different slot widgets available in Protege-2000. Slot widgets are small user-interface plug-ins designed to facilitate the input or display requirements of Protege users. Storage back-end. Description DAML+OIL Crea te and edit DAML+OIL onto log ies with Protege J a v a Funct ion Cal ls S la t Widgets a n d Storage Backend A group of p lug- ins that al lows the descr ip t ion of th ings in f lux, act iv i t ies , and processes wh ich cause a knowledge base to change ove r a t ime scale O W L L o a d , save , and ed i t Web Onto logy Language (OWL) onto loqies in Pro tege. RDF C rea te , import , and save RDF(S) f i les in Protege UML S to re a Protege knowledge base in UML. XMI S to re a Protege knowledge base as XMI f i les . XMI is a s tandard fo rma t for metada ta exchange suppor ted by OMGj t h e group tha t is responsib le for s tandards such as UML, C O R B A and the C o m m o n Warehouse Meta-mode l XML Onto logy S to re a Protege knowledge base in XML. C lasses a re represented in a Sc hema file as types and instances are output into an XML document instance conforming to the genera ted schema XML S c h e m a Sto re a Protege knowledge base in XML. The backend will genera te a n XML S c h e m a file wh ich conforms to the Protege knowledge mode l and an XML file which conta ins c lasses and ins tances. Table 3-8 Storage back-end plug-ins in Protege-2000 These plug-ins allow importing, exporting, and storing ontologies in different formats within Protege. Chapter 3. Methodology 71 Tab J*ig-m Algernon A rule based inference system implemented in Java and interfaced with Protege. Performs -forward and backward rule-based processing of f rame-based knowledge bases Bean Generator Generate h l P A / J A D E compliant ontologies tram Protege projects. BeanShel l Interactively use the Protege Knowledge-Base API. CLIPS Use the CLIPS Rule Engine trom within Protege DataGenie Read data trom an arbitrary database into Protege Eligibility Screening Find a set ot clinical trial protocols in breast cancer tor which a patient might be eligible. ezOWL Visua 1 O W L tweb Onto logy Lang ua geJ editor tor Prote ge. EZPal Facilitate acquisition a t Protege AHiom Language (PALJ constraints wi thoutknowingthe P A L la ng u age Facet Constraints Identity and t i H Instances that have constraint violating tacets. F C A Demonstrate the benefit ot applying F C A while building an ontology Flora A query tab based on F-Logic InstanceTree Provides a tree v i e w ot f rames referenced directly or indirectly by an Instance, Jambalaya Visualize Protege ontologies with SHriMP (Simple Hierarchical Multi-Perspective). JessTab Allows the use o t J e s s and Protege together. O I L Classifier Classify O I L ontologies with the F a C 1 descriptions-logic classifier O K B C Tab Import and e H p o r t ontologies to and trom O K B C servers via the O K B C interface QntoViz Visualize Protege ontologies with the help ot Graph viz graph drawing software P A L E H press constraints about a knowledge base and make logical queries a bout the contents of a knowledge base. Prolog An integration ot G N U Prolog tor Java with Protege PROMPT Manage multiple ontologies, merge separate ontologies to create a single coherent ontology, entrant a part of an ontology, and move f rames f rom an included to an including project P S M Librarian Browse a Problem-Solving Methods library Relations Browse reitied relations in the same way you can browse regular relations Remote KB Create your own tab to browse a remote knowledge source using a standard API and user interface String Search Search all values o t t y p e String in a knowledge base. Search includes classes, slot values, and metaclasses slots, instances. T G V i z T a b Visualize Protege ontologies using the TouchGraph library T M T a b Build an ontology which may be e H p o r t e d as a topic map in X I M syntaH UMLS T a b Search the Unitied Medical Language Sys tem (.UMUSJ and annotate your current Protege ontology with terms, concept ids, synonyms, relations, and other information from UMLS WordNet T a b Search WordNet and annotate your current Protege ontology with terms, concept ids, synonyms, relations, and other information from WordNet X M L Tab EHtract Protege ontologies trom X M L liles and create X M L tiles trom Protege ontologies Table 3-9 Tab plug-ins in Protege-2000 These plug-ins facilitate the inclusion of other applications into Protege-2000. A s mentioned earlier one of the most important features in Protege-2000 is its ability to provide interoperability with other knowledge representation systems. To achieve this, Protege uses a knowledge model compatible with Open Knowledge-Base Connectivity protocol ( O K B C ) . Protege-2000 users can easily import and export ontologies using OKBC-compatible knowledge representation systems [Noy, Fergerson et al. 2000]. The Open Knowledge-Base Connectivity protocol ( O K B C ) is a common query and construction interface for frame-based systems. A knowledge base in a frame-based Chapter 3. Methodology 72 system is built around the notion of frames. A frame is a primitive object that represents an entity in the domain of discourse [OKBC]. The knowledge model used by Protege-2000 is frame-based. A Protege ontology consists of classes, slots, facets, and axioms [Noy, Fergerson et al. 2000; Noy and McGuinness 2001]. Classes describe the concepts in the domain of discourse. Slots refer to various attributes or properties of these concepts and the relations amongst them. Facets present the properties and some restrictions of slots. Axioms specify additional constraints on these slots. Within Protege, an ontology along with a set of individual instances of classes with specific values for slots, form a knowledge base. In this work we will refer to an instantiated ontology as a knowledge base [Noy, Fergerson et al. 2000; Noy and McGuinness 2001; Knublauch 2003]. Figure 3-3 shows a screenshot of the Protege-2000 ontology-editing environment. In the left pane, the class hierarchy is presented. The middle pane shows the list of instances for the selected class. The right pane displays some information about the selected class in detail such as class' slots and their values. I Project Window Half) P A L Constraints TGVtzTab [jb j|gg|ifipl I^ JS] PAL Queues i i : : instancy l i e u L*>dlFah Hev2 • TCMcTab I © Jambalaya XML ' c i : : C l a s s e s & Instances C lasses ' S Slots lirl,iti<.n-,ln|iSuj_. •»• V i| C ' X ® - © ; S Y B T E M - C L A 8 S * © P r o p e r t y (5) ®" © T e m p l a t e • • © T I M E * 9 © P L A C E * © CONTINENT (5) © P R O V I N C E (11) © • © C I T Y (8) © A R E A (3) © C O U N T R Y " (7) • • © A G E N T * © P E R S O N M (64) « > • © SOCIAL-GROUP * M ® - © POSIT ION_CONCEPTS * © E V E N T (70) © - © D O C U M E N T * © T I T L E (11) © - © REFIED-RELATIONS * PAL Constraints ' Relations Qntoviz 'Forms i : : Instances f #4Queries Knowledtje Tree Knowledue Acquisition C l a s s C) CONTINENT DiMtjtQsjtanceSr ¥ P Afr ica ••$> A m e r i c a • A s i a I Aus t ra l i a 4>Eurpoe © C O N T I N E N T (ty|tc SI A N D A R D . C L A S S ) 1MEJ N a m e D o c u m e n t a t i o n ( C O N T I N E N T R o l e j Concrete W | T e m p l a t e S l o t s N a m e 1 T y p e 1 C a 1 R R - c o n s l s t - o f - c o u n t r i e s 1 Ins tance mul t ip l i SJ A - n a m e Str ing s i n g l e JQ R R - w a s - b o m - h e r e 1 Ins tance mu l t iph Si R - e v e n t - h a p p e n e d - a t 1 Ins tance mul t ip l i Si R R - h a s - r e s i d e n t * Ins tance mul t ip l i X R R - d i e d - h e r e 1 Ins tance multiple 4 Figure 3-3 Screenshot of the Protege 2000 development environment Chapter 3. Methodology A n in-depth explanation for these terms is given in the following paragraphs. • Classes 73 Classes represent concepts in the domain of discourse. They can have attributes and relations. In Protege-2000 Classes are arranged in a taxonomic hierarchy. This tool represents the sub-class relation in a tree and also supports multiple inheritances. The root of a class hierarchy is the built-in class called " T H I N G " (Figure 3-3). • Slots In Protege, slots describe properties of classes and instances. They can also be used to build relations and associations between these classes and instances. Slots can be defined independently of any class; this means that they can exist without being assigned to a class. For example a slot called "name" can be defined and later attached to several different classes. Figure 3-4 illustrates an example of a slot which attached to more than one class. S3 J M M M M 20QOAHistorjf Ontot«gy\0<ito.. . _ l 5 ;] Project Window Help PAL Constraints TGVUTab Q P P ! mm tips ' i Instance Tree EZPalTab Rev? TGVtzTat) ® Jatnhalaya XMI Classes & Instances PAL Constraints c Relations Ontow i . Knowledge free - Classes :> Slots I onus r : instances M Queries Knowledue Actiuisttion o * : S T A N D A R D S l . O I ) | V | CJ[Xj» ^1 A-nanie (tyi> l S A - m o n t h - n a m e - M j n » r 1 | £ j N a m e SlArmonth-n^W [§JA-month-tu ** [gJA-montri-vi l&JA-name LSjA-number-D|]A-number-[SjA-number-[SflA-other-rrarj SlA-Position-SlA-position-i (SJA-year-nu (S|A-year-nui SJO A-year-nui C l a s s e s © A G E N T * © POSIT ION © E V E N T TOTITI F N a m e lA -name V a l u e l y istrino Document ;stiort i tp la teA c Mir i i i r iu i i Cardinality • required • multiple Inverse Slot Default at least at most! Figure 3-4 Slots in Protege-2000 In this example, the slot "A-name" (in the left of the screen) is assigned to 5 classes (bottom left). The foreground window presents the information that can be defined for the slot. Chapter 3. Methodology 74 • Facets Facets specify constraints on slot values such as slot's cardinality (number of values that slot can have), slot value type (e.g. integer, string, float, instance of a class), maximum and minimum values for numeric slots, etc. For example, a slot "a-year-number" can be assigned 2 different maximum values depending on the class it is attached to. In Figure 3-5, the maximum value of the slot "a-year-number" can be either 2003 or 1382 depending on the chosen calendar (class it is attached to). Project Window Help PAL Constry—" Q , & ' ; & [ % fi, Relations Ontovfc i Knowle c Classes S Slots ; Q Forms ; Relationship Superclass I® THING*" •"©.SYSTEM-CLASS* ©Property ••©Template ? ©TIME* r ©TIME-ELEMENT* f ©YEAR* ©YEAR-SOLAR ©YEAR-LUNAR © YEAR-CHRISTIAN $ c•• MONTH* ype=-.STANDARD CI, ASS| Documentation Constraints YE AR-SOLAR Role Concrete C + template Slots Name [SJA-year-mimber* Type T Card ina l i ty [C j ) Other Facets Integer single minimurn=1, maximum=1382 Figure 3-5 Facets in Protege-2000 The facet maximum value applied to two classes for the slot "a-year-number". Axioms Protege-2000 does not allow for user defined axioms and rules. Constraints in this environment are limited to those provided by facets. In other words, Axioms and rules Chapter 3. Methodology 75 cannot be explicitly represented in Protege [PAL Documentation]. This could be an issue since, while creating the ontology it is necessary to be able to make general assertions about the fundamental concepts and be able to later test out and ensure that the assertions hold across the entire knowledge-base. For example, consider an ontology in the history domain. This ontology may consist of concepts like Person, Place, Event and it will inherently involve dates and times. It is reasonable that we be able to assert the following, common-sense constraints: o A l l instances of Person have exactly one birth-date. o A Person's birth-date must precede the death-date. o Every Event in which a person is involved, must take place between his/her birth-date and death-date. These constraints ensure a certain level of ontology consistency [PAL Design Rational Document].The primary purpose of the Protege Axiom Language (PAL) is precisely to support the definition of such arbitrary logical constraints on the frames of a knowledge base. P A L constraints are built with special-purpose frames and can be stored as part of a knowledge base. The P A L constraint-checking engine can be run against the knowledge base to detect frames that violate those constraints [PAL]. In P A L , a constraint consists of a set of variable range definitions and a logical statement that holds on those variables (Figure 3-6). The language used by P A L is a limited predicate logic extension of Protege-2000. This language supports the definition of the aforementioned ranges and statements. The syntax of P A L is a variant of the Knowledge Interchange Format (KIF) [PAL Documentation]. KIF is an interchange format, designed to be easy for computers to parse. The P A L implementation of the constraint: " A l l instances of a Person have exactly one birth-date", is presented in Figure 3-6. Chapter 3. Methodology 76 mi niesVProtege ?000\HistDry OntologyvOntotog., Project Window Help PAL Constraints TGVfcrTab PAL Queries ' : Instance Tree EZPalTab Rev2 TGvlzTati © Jamtialaya XML Classes & Instances PAL Const taints ' Relations Ontow/ i. . Knowledge Ttee Classes S Slots " Fturns r Instances #% Queries Knowledge Acquisition Choose Constraints Evaluate ? Status \ v w m v c - x Constraint f v Only One birth-date > Description Warn about Indicated cons! Only One birth-date Attachments for selected ctmstratf Tracing Controls • Trace during evaluation function to Trace Predicate to Trace Sran-.iift.tivJ> () () ,% ft foral X ?X (exists ft (birth-date ?X ?Y))) the constraints concers all instances of the PERSON class, and any Instance of the DATE class The statement will check that all instances of Person have exactly one birth-date Ranrje (derrange ?X :FRAME PERSOH) (defrange ?Y :FRUi£ DATE) Figure 3-6 Defining axioms in Protege-2000 In this figure, we define two variables: ?X and ?Y. ?X ranges over instances of Person. ?Y ranges over instances of Date. We then assert that associated to every ?X, there is a ?Y. • Knowledge-acquisition forms Protege-2000 uses knowledge-acquisition forms to attain information about instances. Protege relies on a form-based interface as the central user-interface metaphor [Grosso, Eriksson et al. 1999]. A user can define a class and attach template slots to it. Protege will then automatically generate a form to acquire instances of that class. The slots for this class, their cardinality and value type will determine the default layout and content of the generated form. Users can later customize this automatically generated form for each class to better suit the requirements of the specific class. Figure 3-7 shows an example of these forms. Chapter 3. Methodology 77 ?• OntologyVersionl 3 Protege-2000 (F;tf>rogram Fi'les\Protege-2000\History ( IntologyVOritologyVersioiil... _ ' G J X Project Window Help PAL Constraints |ojf£|»f] g j fc j c i . : instance Tree ! EZPalTab Rev2 • lGVizTah © Jatnnalaya ' XML i Classes & Instances PAL Constraints Relations Gntoviz i : ; Knowledge Tree PAL Queries [ c Classes S Slots Forms j i:: Instances ft Queries Knowledge Acquisition | Forms | X | j f i g % J Form Browser Key SYSTEM-CLASS Property0 11 Template ©• II T I M E ©• 11 P L A C E O ^ A O E N T C • P E R S O N " C 11 SOCIAL-GROUP " ° ©- II POSITION.C0NCEPTS I EVENT0 ©-H DOCUMENT0 §1 TITLE0 © • S R E F I E D - R E U T O N S i Figure 3-7 A knowledge acquisition form in Protege-2000 This figure presents the generated form for the class "PLACE". • Meta-classes Protege-2000 supports a flexible meta-class architecture which uses configurable templates to define new classes in the knowledge base. The use of meta-classes allows for extensibility and enables interoperability with other knowledge models [Noy, Fergerson et al. 2000]. A meta-class is a class whose instances are themselves classes. A meta-class is a template for classes that are its instances, it describes how a class that instantiates the template will look. In Protege-2000, every class is both a subclass of a class in the class hierarchy, its super-class, and it is an instance of another class, its meta-class. By default, Protege classes are an instance of the : STANDARD-CLASS meta-class (Figure 3-8). Chapter 3. Methodology 78 "f- OntologyVersioii'12 Protege-2000 (F:\Program Fites\Protege?000Wistory Onfotogy\OntologyVersion1 P.pprj) Project Window Help PAL Constraints TGVuTab mm mm c Relations Ontovw i: Knowledge Tree PAL Queries i instance Tree ; EZPalTdb Hev2 IGVuIab © Jamualaya XML c~ Classes S Slots ; _ £ Forms i . Instances #4 Queries Krtowledije Acquisition c 1:1 Classes & Instances PAL Constraints Krlfltmnsrm:' Superclass " VlC f ©'SYSTEM-CLASS* © ©.CLASS* • © :STANDARD-CLA3S © QUERYABLE-CLA88 ©Template MetaCiass ©test-metaclass © • © : S L 0 T * ©•@:FAC£T* ©• @ .CONSTRAINT* ©•©ANNOTATION* ©•©DELATION* ©•©QUERY* ©Property ©•©Template © © T I M E * ©©PLACE* ©•©AGENT* ©PERSON M ©•©SOCIAL-GROUP** ©• (ci eoataofei COMBBBB * [TIME Rote Abstract* template Slots Name Documentation jlEj Constraints TIME is an abstract superclass fori all Urns related concepts. _Cardjnali^_ Other Figure 3-8 Meta Class ":STANDARD CLASS" in Protege-2000 The class TIME is a sub-class and instance of STANDARD CLASS. Protege-2000 allows users to define their own meta-classes and to define new classes as instances of these user-defined meta-classes. Users can later customize the forms to acquire instances of these meta-classes, which are new classes in the ontology, effectively creating new ontology editors [Noy, Fergerson et al. 2000]. Figure 3-9 shows a user customized class form to acquire the name of the author of the class in addition to the included information from the STANDARD CLASS. Chapter 3. Methodology 79 W- UntotogyVersirml2 Protege^ 2000 (F:\Progrnm Files\Protege ?000tf)istory Onfofogy\OntologyVersion1 2.pnrj) Project Window Help PAL Constraints TGVizTab Otduvu : Knowledge Tree PAL Queries > Instance Tree EZPalTal) Rcv2 ICVizrau © Jaroualaya XML S Slots " F o r m s i::instances #4 Queries ' Knowledge Acquisition i . Classes & Instances ' PAL Consti RetauonsniMJSuperclass • J V| C |© :THING* « © .SYSTEM-CLASS * y ©:CLAS8* f ©:STANDARD-CLASS © QUERYABLE-CLASS ©Template MetaCiass ©test-metaclass • @:SLOT* • ©:FACET* • ©:CONSTRAINT* ©•©ANNOTATION* • © DELATION* • © Q U E R Y * © Property ©•©Template • © T I M E * • ©PLACE* • © A G E N T * © P E R S O N " • ©SOCIAL-GROUP*" |.ifriamsmoN C H N C F P T R * Name Role moment atton traints |c|x] Cemr i raMtsb i Concrete Template Slots Author C Figure 3-9 An example of user-defined meta-class in Protege-2000 The meta-class architecture in Protege-2000 allows developers to adapt the tool to create and edit knowledge bases with knowledge models that are different from the Protege-2000 knowledge model. An example of this is the adaptation of Protege-2000 to become an editor for Resource Description Framework (RDF) Schema and RDF instance data [Protege-2000/RDF 2001]. Protege-2000 can translate an RDF knowledge base created in Protege-2000 into standard RDF syntax; effectively making Protege-2000 an editor for RDF documents [Noy, Fergerson et al. 2000; Knublauch 2003]. RDF is a knowledge representation standard being defined by the World-Wide Web Consortium [W3C/RDF 2000]. The main purpose behind developing RDF is to make information available in the Web not only human-readable but also machine-readable. Protege-2000 also complies with the new OWL (Web Ontology Language) knowledge model, which is developed by the World-Wide Web consortium and is emerging as the standard for defining metadata for encoding machine-readable semantics on the Web [Protege-2000/OWL 2003]. Chapter 3. Methodology 80 3.1.3 Ontology Evaluation In order to evaluate the correctness and completeness of the created ontology, we use the query and visualization facilities provided by Protege-2000 along with the set of motivating scenarios and competency questions which were developed in the domain analysis stage. In order to do so, we first instantiate the ontology and examine whether the ontology provides support for the scenarios and is able to answer each and every competency question. We use the built-in query engine in Protege for the simple query searches and use the P A L query plug-in to create more sophisticated searches. We also use protege-visualization plug-ins to brows the ontology and ensure its consistency. Chapter 4. Build a history ontology 81 4 Build a history ontology In order to build an ontology for a historical document, we chose to follow a series of stages as described in the previous chapter. In this chapter, we will describe the procedure undertaken to build the ontology and provide the results obtained for each step carried out throughout the ontology development process. These steps are exactly those outlined in chapter 3 and include: identify the purpose and intended users, domain analysis and knowledge acquisition, building a conceptual ontology, building a formal ontology, and ontology evaluation. A brief explanation and the results obtained for each of these stages of our ontology building process are presented in the following sections. Since our chosen methodology is based on an iterative-evolving process only the final results for each stage is presented. Every step of the process is explained briefly since it has already been described in detail in chapter 3. 4.1 Identify the purposed scope, and intended users The purpose of this stage is to identify the purpose, scope, and intended users for the ontology that we are about to build. In order to do this we provided answers to each of the following questions: Question 1: For what purpose is the ontology being developed? Considering the conventional ontology development purposes stated in the previous chapter we designed this ontology to facilitate the following: • Allow communication between people who have an interest in historical documents. By this, we mean that people within a community should be able to use the same terminology to refer to the concepts with the same meaning within the domain of discourse. Furthermore users of this model should have access to the semantic of a document to refer to these concepts. • Enable interoperability amongst systems. By using the same knowledge model computer systems will be able to use this ontology and apply their own applications on it. Chapter 4. Build a history ontology 82 • Ensure reusability. The ontology is designed so it can be shared amongst people and systems and also designed in a way that facilitates later integration into other ontologies and thus allow its reuse. • Facilitate knowledge acquisition. This is one of the main goals our work. Knowledge found in documents can be hard to extract. Much of the meaning behind passages and sections of documents can be hidden amongst tons of words. One of our goals is to represent the semantic within a historical document. In other words, we mean to identify and represent the main concepts in this document along with their relations. Another goal of this work is to represent the temporal aspect of the knowledge. This refers to capturing the dynamicity of the stated relations within a time-line. Question 2: What is the domain that the ontology will cover? In order to test our ideas, we selected a history book as our test base. The book, "History of Iranian Constitution", is written by "Ahmad Kasravi" and printed in Farsi. It talks about the events that led to the Iranian constitution. The book talks about the people who were involved in these events, the places where they happened, and their consequences. It also discusses the evolution of the governmental hierarchy and how people in this hierarchy have taken over each other's positions throughout time. In short, the domain that this ontology aims to represent is that of a historical document, specifically a short range of the history of the Iranian constitution that spans for about 50 years. Question 3: What type of questions must the information in the ontolosy answer? In order to answer this question we devised a set of competency questions and motivating scenarios (section 3.1.1). Table 4-1 shows a list of the competency questions that we kept in mind when we started this project. This list was later modified to that shown in Table 4-3 to Table 4-6. Chapter 4. Build a history ontology 83 List of Competency Questions (first draft) 1. Who is person P? 2. In what events has person P been involved? 3. What was person P' s role in event E? 4. What is the relation betweenperson PI and person P2? 5. What is the relation betweenperson PI and Group G? 6. Atfzwe TI who is person PI related to? 7. What statements did person PI make? 8. To which eve«£ person P 's statement S was related to? 9. What£>osi£io«s has person P held? 10. When did person P hold these positionsl 11. J^ %o was taking over person V 5 position PO? 12. Who were;?greo« P's superior and/or inferior? 13. What was event E about? 14. Who was involved in event E? 15. Where did event E take place? 16. When did event E take place? 17. What were the consequences of event E? 18. Is there any relation between events E l and E2? 19. What events happened at location L? 20. What is the geographical hierarchy of location L at time T? 21. Who was from location L? Table 4-1 First draft of the competency questions These are the questions that the ontology must be able to provide answers for. Some of the motivating scenarios contemplated whilst developing this ontology are presented in Table 4-2. Chapter 4. Build a history ontology 84 Motivating Scenarios A person doing a biography of any person represented in the book will be interested in this person's date of birth, place of birth, events in which he/she participated, as well as the different roles played within the different organizations that he/she belonged to. Far the general public a user might be interested in a person's ranking in the government or social status in any given timeframe and how this ranking or titles might have changed throughout history. These users might want to find out about a particular person and this person's involvement in a particular event. An archeologist might be interested in a particular place or location; it would be useful for him to know which events happened in this place and who lived there through out time. Another aspect which might be of importance to an archeologist is the geographical hierarchy of places throughout time. In the case of a historian, it might be of interest to know about a particular person P who held position PO in the government. The user might be interested in people whom this person was involved with, in particular those directly above or below in the hierarchical government structure. This user might also be interested in getting an overview of the hierarchical structure of the organization during the time that person P was involved in it and how this hierarchical structure changed over time. A historian might also be interested in the hierarchy of the royal family: who was the king, who were his sons, when any of these took power. Yet another aspect of interest might be who took over the different social positions, and during which time or event. Table 4-2 Motivating Scenarios Some of the scenarios that the developed ontology must provide support for Question 4: Who will use the ontology? (Identify and characterize the range of intended users) Since this ontology is intended as a proof of concept and not necessarily meant to be used in practice, the selected intended audience is that of the general public who might be interested in reading the book but want to obtain more information than that which is attainable by using conventional keyword search. Other people who might benefit from this ontology are researchers or historians interested in the semantic behind the words in the book. Chapter 4. Build a history ontology 85 Question five: What is the level of formality required for the ontology? Our approach utilizes both an informal and a formal representation at different stages of the development process. First, we develop an informal model (conceptual ontology), which is later instantiated and transformed into a formal ontology by utilizing the Protege-2000 development environment (section 3.1.2.4.1). 4.2 Ontology building In this stage, we first analyzed the domain and performed several knowledge acquisition methods (as described in 3.1.2.1) to extract the knowledge required to build the ontology. We then used this knowledge to build our conceptual ontology which was later formalized, instantiated, and evaluated using Protege-2000. 4.2.1 Domain analysis and knowledge acquisition In this stage, we first expanded our competency questions to cover all the aspects of the information that must be included in our ontology. Table 4-3 to Table 4-6 show our extended version of the competency questions. This list of competency questions is organized by the general or top-level notion that they refer to. These top-level notions were defined later in the development process however they are used here for clarity purposes. List of Competency Questions (PLACE) 1. What type of place is place P? {continent, country, province, city, area) 2. Where is place P located? (in which continent, country, country, province, city...) 3. Who was born in place P? 4. What events happened at place P? 5. If place P is a country, which are the neighbors? 6. What changes have occurred to place P (its name, ownership, changes in geographical hierarchy??!!!) Table 4-3 Competency questions related to the notion "PLACE" Chapter 4. Build a history ontology 86 List of Competency Questions (EVENT) 1. What was event E about? 2. When/Where did event E take place? 3. Who (which countries) was/were involved in event E/ and in what role? 4- What were the consequences of event E? 5. What weretheprecedents of event E? 6. What other events is event E related to? (what are the relations?) 7. What is the relation between event E l and E2? 8. What other events took place at the same time as event E? 9. Is event E a composite of other events? If so what are those events? 10. Who holds position PO during event E? 11. What statements were published related to event E? 12 Who was in opposition to / in favor of event E? Table 4-4 Competency questions related to the notion "EVENT" List of Competency Questions (PERSON) 1. Who is person P? 2. Where/when was person P born? 3. Where/when did person P die? 4. What title-of-honor did person P have? and for how longl 5. What positions did person P hold? 6. Who else lived in the same era as person P? 7. What was the relation between person PI with Person P2 or Group of people G? How long did the relation last? 8. Who belongs to group G? 9. What type of group is group G? (social group? Religious group? Political group?) 10. For How ions, did person P hold position PO? Start-date? End-date? Duration? 11 Who else had the same position PO as person P? 12. Who are the inferiors and superiors of person P in the hierarchy? 13. When was person P dismissed from position PO? Who took over position PO? Table 4-5 Competency questions related to the notion "PERSON" Chapter 4. Build a history ontology 87 List of Competency Questions (DOCUMENT) 1. What was document D about? 2. Who made document D? 3. When was document D made? 4. What type of document is document D? 5. In relation to what event(s) was document D done? 6. What are other documents with the same subject or about the same event as document EJ? Table 4-6 Competency questions related to the notion "DOCUMENT" We used brainstorming sessions in conjunction with these competency questions and motivating scenarios to extract all potentially relevant terms for our ontology. These terms were gathered into a glossary. This glossary of terms includes the terms, their definition or description, and may include additional information such as examples that help understanding these definitions. In order to provide a definition for the terms, we consulted dictionaries such as the Merriam Webster Dictionary [Merriam] and the Oxford Dictionary [Oxford] as well as general purpose ontologies such as SUMO [SUMO], Ontolingua [Ontolingua], and WordNet [WordNet]. We must note that this was an iterative process and as we proceeded in our development, these lists (competency questions, motivating scenarios and glossary of terms) evolved. Table 4-7 shows a partial view of our term glossary. Chapter 4. Build a history ontoloRy 88 Glossary of Terms Term Definition Resource Agent "Sometning or someone that can act on its own and produce changes in the world." SUMO Person An individual, someone, somebody. An agent with certain rights and responsibilities and the ability to reason, deliberate, make plans, etc. This is essentially the legal/ethical notion o f a person WordNet & SUMO Group-of-People A number of individuals assembled together or having some urufying relationship Merriam Webster Religious Group A Group-of-People whose members shareasetof religious beliefs SUMO Government A ruling body of a country Oxford Position A formal position of responsibility within an organization. SUMO Event Sometiiing that happens at a given place and time and has a certain duration. SUMO & WordNet Place A particular region, center of population, any geographic area which is associated with some sort of political structure. This notion includes Lands, Cities, districts of cities, counties, etc. Merriam Webster & SUMO Time-Point TIME POINT is a specification o f a single point in historical time. A time-point is not a measurement of time, nor is it a specification of time. Ontolingua & SUMO Table 4-7 Partial view of the glossary of terms 4.2.2 Building an informal ontology Once we obtained a relatively complete list of competency questions and glossary of terms, we identified concepts, relations within the concepts, and their attributes. We did this according to the guideline presented in the previous chapter (section 3.1.2.3). In our lists of competency questions (Table 4-3 to Table 4-6) concepts are shown in italics and the relations are underlined. The concepts and their related properties are stored into concept dictionaries which are structured into naturally occurring groups. This approach is a combination of the approaches introduced in [Noy and McGuinness 2001] and those of [Lopez, Perez et al. 1999]. At this stage we categorized our concepts into Chapter 4. Build a history ontology 89 five concept dictionaries relating to people, places, events, documents, and time. Each of these categories holds the concepts that are most related together. In Table 4-8 to Table 4-12, the relations and attributes specific to each particular concept are shown in italics. The rest (non-italic) are shared amongst all the concepts in the same dictionary. Table 4-8 to Table 4-12 illustrate our concept dictionaries. Each of the tables is preceded by a brief description. Further explanation will be provided later when we demonstrate the conceptual model based on these concept dictionaries and whilst transforming the conceptual ontology into a formal ontology. Table 4-8 shows concepts related to the notion " P L A C E " . Within our domain, we identified five different types of geographical places: continent, country, province, city, and an area within a city. The relations that are represented here include those that capture geographical interdependencies amongst the different type of places, those that present a connection between places and events, and those that demonstrate the association between people and places. Chapter 4. Build a history ontology 90 Concept Dictionary for the notion "PLACE" Concept N a m e Property Relation C O N T I N E N T has-name event-happened-in , people-was-born-in, people-lives-in, people-died-here, countries-included C O U N T R Y has-name eve nt-happ e ne d- in, p e op 1 e -was -b orn-in, "people-lives-in, people-died-here, has-neighbdr, consist-of-pravinces, located-in-continent, P R O V I N C E has-name eve nt-happ e ne d- in, p e op 1 e -was -b orn-in, people-lives-in, people-died-here, consLst-qf-cities, located-in -country, C I T Y has-name eve nt-happ e ne d- in, people -was -b orn-in, people-lives-in, people-died-here, consist-of-areas, located-in-p rovince A R E A has-name eve nt-happ e ne d- in, p e op 1 e -was -b or n-in, people-lives-in, people-died-here, located-in-city Table 4-8 Concept dictionary related to the notion "PLACE" Table 4-9 illustrates the concepts related to people. This includes both individual persons and groups of people. In our work, we identified three concepts that are associated with people: individual persons, groups of people, and social/governmental positions that a person may have. As for relations amongst these concepts, we included those that represent the associations between a person and a group of people, those that denote relationships amongst a place, a person, and/or a group of people, and those that are specific to each of these concepts such as a particular relation that shows the positions held by a person or the foundation date of a group. We should note that, this table does not show neither the hierarchical structure of a position concept nor the changes this hierarchy might have undergone throughout time, this will be presented later when we describe the conceptual ontology model. Chapter 4. Build a history ontology 91 Concept Dictionary for the notion "PEOPLE" Concept Name Property Relation PERSON name other name description gender i s -re lat e d-to - do cume nt, made - st ate m e nt, is-addressee-of, involved-in, is-Jather-of, is-son-of, is-father-in-law, is-son-in-law, holds-position, is-member-of, is-addre ssee-qf-statement, has-birth-date, has-death-date, has-birth-place, has-death-place, has-title-of-honor, POSITION name description position-level p o s iti o n-ho lde r, has -tim e - inte rval GROUP- OF-PEOPLE name other name description group-type i s -re lat e d-to - do cume nt, made - st ate m e nt, is-addressee-of, involved-in, has-joundation-date, has-dismis•sing-date has-member Table 4-9 Concept dictionary related to the notion "PEOPLE" Table 4-10 shows the properties and relations assigned to the concept "EVENT". The relations defined, include those that represent the association of an event with other concepts such as places, people, and documents and those that capture the interrelation amongst events themselves. We consider that events can be a precedence, consequence, part of, and /or composite of other events. We also allow representing whether any given event is related to any other event in any other way. Concept Dictionary for the notion "EVENT" Concept Name Property Relation EVENT name description goal happ e ne d- at-p lac e, happ e ne d- at-time -p o int has-agent, precedence-of, consequence-of part-of, composite-of, has-related-event has -re 1 ate d- do c ume nt, has -tim e -range Table 4-10 Concept dictionary related to the notion "EVENT" Chapter 4. Build a history ontology 92 Table 4-11 shows the properties and relations associated with the concept "DOCUMENT". The relations consist of those that represent the relations between people, events, and other documents to a document. The properties assigned to this concept aim to capture the general information about a document such as its title, a brief description, its content, and its type. Different document types in our domain include: report, letter, telegraph, order, notice, license, contract, memo, agenda, meeting minute, bill, and expense statement. Concept Dictionary for the notion "DOCUMENT" Concept N a m e Property Relation D O C U M E N T title description content document-type publication-date, made-by, made-about-event related-to-document, re 1 ated-agent related-event Table 4-11 Concept dictionary related to the notion "DOCUMENT" Table 4-12 presents all the concepts related to the notion "TIME". These concepts include time elements such as year, month, and day and other time related concepts such as calendar date, time interval, and duration. A calendar date is a time point with a resolution of days. It consists of a day, a month, and a year. A time interval captures a certain period of time which consists of a start time, an end time, and a duration. A duration represents the length of a time interval in form of number of days, months, and years. Chapter 4. Build a history ontology 93 Concept Dictionary for the notion "TIME" Concept N a m e Property Relation Y E A R year-number M O N T H month-number month-name D A Y weekday-name we ekday-numb er mo nth- day- name C A L E N D A R D A T E has-day, has-mo nth, has-year T I M E I N T E R V A L has-start-time, has-end-time, has-duration D U R A T I O N number-of-days numb er- o f-mo nths number-of-years Table 4-12 Concept dictionary related to the notion "TIME" The next step in our process was to use the identified concepts and relations (concept dictionaries) within our domain along with the motivating scenarios to develop our conceptual ontology model. This was carried out in a manner similar to what was presented in the previous chapter (section 3.1.2.3). This conceptual model illustrates not only the concept hierarchy (sub-concepts, super-concepts) but also the interrelations that hold amongst these concepts. We used a middle-out approach to categorize the concepts. The middle-out approach operates by identifying the most important concepts first and then generalizing or specializing the concepts within groups from this point. We also created abstract concepts as organizing features. These concepts are organized as groups due to the similar features that they possess, however they are not directly related as super-concepts and sub-concepts. For example, we grouped the concepts related to time under a super-concept TIME. (Figure 4-3) The next stage in our process is to build the conceptual model of our ontology. Figure 4-1 to Figure 4-13 represent the different parts of our conceptual model. A detailed explanation is provided prior to the presentation of each of these figures. We adapt a simple Entity Relationship (ER) model to illustrate our conceptual ontology at this stage. Within these figures, a rectangular shape represents a concept, a diamond symbolizes a Chapter 4. Build a history ontology 94 relationship, and an oval shape denotes the attributes associated with these concepts or relations. These attributes can be concepts themselves such as concept "TIME" which can be allied with relations. Some of the relations denoted by a diamond contain the symbol "/", which indicates that the relation is bidirectional. In other words, the stated relationship has an inverse. Throughout the development of our ontology we searched existing libraries of ontologies in order to find similar related concepts or relations useful to us. The individual models we adapted to our own work are cited in the corresponding section. Figure 4-1 represents the top-level concept hierarchy in our domain. Considering the glossary of terms, competency questions, motivating scenarios, and concept dictionaries produced in the previous steps, we identified five central concepts within our ontology: AGENT, P L A C E , EVENT, DOCUMENT, and TIME. Every other concept in this domain is defined around these primitive concepts. PLACE EVENT DOCUMENT AGENT TIME Figure 4-1 Main concepts within our ontology Figure 4-2 roughly illustrates the relations that hold amongst the main concepts. These concepts and relations are presented in detail when we represent the conceptual model for each of these concepts. At this point, we try to give the reader an overview of how these concepts are related to one another. Chapter 4. Build a history ontology 95 Figure 4-2 Overview of main concepts and relations in our history ontology The doted- lines denote the existence of internal relations within a concept. The time concept associated with the relations indicates that a particular relation is time-dependent. The "is-a" relation shows how bottom-level concepts are a type-of top-level concept. The representation of time is fundamental to any knowledge model that aims to represent change or action. Many ontologies that try to represent time are currently available. Some examples of these include: Simple-Time Ontology form Ontolingua Sever [Ontolingua], Time Ontology from SUMO [SUMO], and the Time ontology developed in the Stanford Knowledge Systems Laboratory [Zhou and Fikes 2002]. In order to develop our time model, we studied these existing time ontologies. We based our work on these ontologies and adapted them to fit our needs. Traditionally time ontologies have a resolution of seconds or. even milliseconds, however our time model has a coarser granularity and measures time by day. Chapter 4. Build a history ontology 96 Our time model is illustrated in Figure 4-3. It considers time as an infinite continuum. Any single point on this continuum is a TIME-POINT (i.e. Jan 1, 1900). If we have two TIME-POINTs we can describe a TIME-INTERVAL (i.e. from Jan 1, 1900 to Aug 1, 1900) and calculate a DURATION (seven months). Note we can have a DURATION with unknown TIME-POINTs or INTERVAL. In our representation of time "TIME POINT" and "TIME I N T E R V A L " are the two fundamental concepts. An abstract concept called "TIME" was created and is used as an organizing feature to gather all concepts related to time in a group. Moving down in the concept hierarchy tree we can find C A L E N D A R - D A T E . This concept is a time point with resolution of days. It is the main element used to capture the temporal aspects of our domain. A " C A L E N D A R - D A T E " contains a day, month, and a year. Since the book that we were extracting the data from represents the dates in three different calendars: Solar calendar, Lunar calendar, and Christian calendar, at later stages we defined additional concepts that allow us to represent these three different calendars (Figure 4-4). TIME ELEMENT YEAR DAY MONTH TIME POINT CALENDAR DATE TIME INTERVAL CLEHDAR DATE (startdate) -has—, CLEMDAR DATE (end date) -I—has'-i-L (MONTH) (^DAY) Figure 4-3 Time model in our domain Chapter 4. Build a history ontology 97 -IS-A-i—has-day-name-LUNAR CALENDAR DATE has-day-name CALENDAR DATE -IS-A--has-day-number-DAY WEEK has-year. -IS-A-•has-year I t I J IS-A I—I •has-month YEAR -ISA-DAY LUNAR - I S A -YEAR LUNAR SOLAR CALENDAR DATE —has-month-has-day-name-IS-A 2. MONTH CHRISTIAN CALENDAR DATE DAY SOLAR ISA YEAR SOLAR MONTH LUNAR DAY MONTH Figure 4-4 A CALENDAR DATE within our history ontology CALENDAR DATE is the main element employed to capture the temporal aspects of our domain. As shown, it consists of a YEAR, MONTH, and DAY. Our representation allows us to capture a DATE in either a Solar calendar, a Lunar calendar, or a Christian calendar. Figure 4-5 and Figure 4-6 illustrate our conceptual model for the notion " P L A C E " . In order to construct this model we consulted existing ontologies for geographic information representation and categorization [Alani, Jones et al. 2000; EuroConference 2000; Mark, Skupin et al. 2001; Islam, Bermudez et al. 2003]. People in the geosciences community usually utilize ontologies to build a common terminology to refer to the concepts in that (geosciences, geography) domain. These ontologies are also used to capture the semantic of the relationships between concepts and therefore facilitate the detection of associations between related terms [Alani, Jones et al. 2000]. These geographic ontologies use a level of detail beyond that which we require for our purposes. These ontologies were used to gain an insight in order to develop our simple model which we refer to as " P L A C E " . The main concepts within our " P L A C E " model are geopolitical land areas such as; continents, countries, provinces, cities, and areas within these cities. These concepts relate to the super-concept " P L A C E " through "is-a" relations. This means that the concepts are a kind-of place. Within the concepts, consist-of71ocated-at relations associate concepts to one another. For example, a country consists of one or several cities and it is Chapter 4. Build a history ontology 98 located in a continent. This consist-of relation is commonly referred to as a part-whole relation. These relations are usually employed to organize knowledge about the concepts in a domain. However; ontologies do not have this relation as a built-in functionality unlike the IS-A relation, thus it has to be defined manually [Noy and Hafher 1997]. Since our model is temporally dynamic these relations have a time property associated with them. By temporally dynamic, we mean that the relations within the concepts are time-based, they might change or evolve over time. Additionally, we might also see some new places appear and others cease to exist after a certain time or either their name or region might be changed. For example the cities in a country might change their name, location or might end up belonging to a different country at different points in time. This will be further explained as we describe the transformation of our informal model to a formal ontology. Figure 4-6 shows the relations that hold between the concept " P L A C E " and other concepts in our domain such as PEOPLE or EVENTs. It should be noted that these relations are time-dependent and thus have a time attribute associated to them. CONTINENT COUNTRY P L A C E PROVINCE CITY ( TIME y A R E A ( TIME y ( TIME y Figure 4-5 Interrelations amongst concepts related to "PLACE" Chapter 4 . Build a history ontology 99 This figure represents the interrelations amongst the concepts related to place. These relations allow us to capture the hierarchy of places within our ontology. PERSON (TIME ) PLACE COUNTRY (TIME ), EVENT Figure 4-6 Relations between the concept "PLACE" and other concepts within our ontology Figure 4 - 7 and Figure 4 - 8 illustrate the concepts and relations associated to people. This includes both individual persons and groups of people. Figure 4 - 7 shows an overview of our concept hierarchy. We defined a general concept " A G E N T " referred to as: "something or someone that can act on its own and produce changes in the world". The concept " A G E N T " acts as a super-concept for both persons and groups-of-people. As it can be noticed, the relations that are shared amongst all the sub-concepts of " A G E N T " are only assigned to the concept "AGENT". These relations (i.e. a certain person can make a certain statement due to the relation that exists between " A G E N T " and "DOCUMENT") are inherited by sub-concepts of " A G E N T " ("PERSON", "GROUP OF PEOPLE"). We later added the concept " C O U N T R Y " as a sub-concept for "AGENT" , this was done due to the role that a government of a country might play as the representative of the people within the country in an international affair. A logical consequence of this is to consider the concept " C O U N T R Y " as a sub-concept of both " P L A C E " and "AGENT" . Figure 4 - 8 provides a more in depth view of the relationship between a "PERSON" or "GROUP OF PEOPLE" with other concepts in the domain. Two concepts; "TITLE" and "POSITION" are associated with a "PERSON". The concept "TITLE" captures the titles of honor a person might have for any period of time. These titles are assigned to different Chapter 4. Build a history ontology 100 people throughout history. The notion POSITION indicates the positions that a person might have within an organization. This concept will be further explained in the following section. Figure 4-7 Concept hierarchy for "AGENT," "PERSON, ""GROUP OF PEOPLE," and "COUNTRY" Chapter 4. Build a history ontology 101 TIME TIME TIME Figure 4-8 Relations between "PERSON" and "GROUP OF PEOPLE" and other concepts in our domain Figure 4-9 and Figure 4-10 demonstrate the conceptual model for the notion "POSITION". Within our domain a position is defined as "a formal role with responsibilities that a person can have within an organization." We identified two types of position hierarchies within our history book: governmental positions such as king, prime minister, or governor, and royal court positions such as king and crown prince. Figure 4-9 illustrates how we defined our position hierarchy. Each position has a person assigned to it, who holds the position for a period of time. Therefore there exists a triplet of person, position, and time (or more precisely a time interval) which represents each position at any given point in history. For each position there might also exist an inferior and/or superior which itself consists of a person, position, and time. The reason to represent the positions in this manner is to facilitate building a hierarchical structure of positions that captures the dynamicity inherent to these notions. Our model not only captures how each position is filled throughout time but also how the relations between these positions evolve. Figure 4-10 illustrates our approach for capturing position hierarchies in time. In order to capture the dynamicity of the hierarchy of positions and the people that hold them, we defined a different set of positions that exist at the different Chapter 4. Build a history ontology 102 time slots. By this we mean that, as soon as there is a change in the position hierarchy (like a position has been added, one is removed, the order is changed) we use a new set of positions which are applicable at the new time range. In this set, the positions are labeled according to their rank in the hierarchy. We then build our position hierarchy based on this set and associate the triplet of person, position, and time to this new hierarchy. This will further explained while we constructing our formal ontology. P E R S O N POSITION -(^TIME^) Figure 4-9 Time-based hierarchical relationship between a PERSON and POSITION f^TIME^) POSITION HIERARCHY (JTIME^) PERSON H^TIME^) POSITION POSITION (™T) Figure 4-10 Conceptual model for position hierarchy Chapter 4. Build a history ontology 103 Our representation deals with EVENTs using a set of relations adapted from John Sowa's work on thematic roles or case relations [Sowa 2000a]. Figure 4-11 and Figure 4-12 demonstrate our " E V E N T " conceptual model. The relationships defined for the concept " E V E N T " allow us to capture the who, what, when, where, and why (goal) of an " E V E N T " (Figure 4-12). This model also captures the relationships between different events. Additionally, the time concept assigned to these relations allows us to model chronological, sequential, series, and parallel events (Figure 4-11). Figure 4-11 Interrelations amongst events Chapter 4. Build a history ontology 104 Figure 4-12 Association of an "EVENT" with other concepts in our domain The conceptual model of the " D O C U M E N T " concept is illustrated in Figure 4-13. This model represents the relations that may exist between a document and other concepts in our domain. A l l these relationships have an inverse (i.e. made-by/makes). Later in the development process we defined two sub-concepts of "DOCUMENT" , those referring to documents that have addressees ( M U T U A L DOCUMENTS) and those without addressees (NON-MUTUAL DOCUMENTS). DOCUMENT DATE EVENT AGENT AGENT EVENT Figure 4-13 Concept "DOCUMENT" and its relation with other concepts in the domain Chapter 4. Build a history ontology 105 4.2.3 Building a formal ontology model Once we have created our conceptual model, we utilized Protege-2000 to build our formal ontology. The first step in this formalization is to map the created conceptual model to the model provided by Protege-2000. Table 4-13 illustrates the mapping between the notions we used to describe an ontology and the representation of these notions in Protege-2000. A n in depth explanation of these notions can be found in the previous chapter (section 3.1.2.4). Our terminology Representation in Protege-2000 Concept Class Relation Slot Property / attribute Slot Constraint / Axiom Facet Axiom Instance Instance Table 4-13 Mapping between the terminology we used and Protege-2000 terminology The rest of this section describes each of the steps of the procedure carried out to build our formal ontology. 4.2.3.1 Mapping our domain concepts to a class hierarchy At this stage we transform our conceptual model to the class hierarchy in Protege-2000. The class hierarchies are illustrated in Figure 4-14. Chapter 4. Build a history ontology 106 (eg) Classes | Relationship Superclass I):THiNG* ©•©:SYSTEM-CLASS* © • © T I M E * © - © P L A C E * ®" © A G E N T * 0 © POSmON-RELATED-CONCEPTS* 1 © EVENT © • © D O C U M E N T * © T I T L E (a) " V C Ar-te Classes {C} (c Classes {to) Relationship: c 9 © T I M E * f- ©TIME-ELEMENT* | 9 - © Y E A R * ; ©YEAR-SOLAR I ©YEAR-LUNAR ©YEAR-CHRISTIAN 9 © M O N T H * ' '•• ©MONTH-SOLAR ; © MONTH-LUNAR L © MONTH-CHRISTIAN f © D A Y E L E M E N T * 9 - © D A Y - W E E K * 1 1 ©DAY-SOLAR ! I ©DAY-LUNAR ! 1 © DAY-CHRISTIAN ©DAY-MONTH © T I M E POINT* 9 © C A L E N D A R - D A T E * ! © SOALR-CALENDAR-DATE | - © LUNAR-CALENDAR-DATE ! 1 © CHRISTAIN-CALENDAR-DATE © D A T E © T I M E RANGE © D U R A T I O N • . . . Superclass © • © : S Y S T E M - C L A S S * © • © T I M E * 9" © P L A C E * | i © C O N T I N E N T | \ © P R O V I N C E 1 h < § > C I T Y ' : © A R E A 1 © C O U N T R Y " f © A G E N T * : © P E R S O N \ 9 © G R O U P - O F - P E O P L E * j | L © RELIGIOUS J3ROUP j | I © POUTICAL.OROUP j I * © O T H E R - G R O U P I ! © C O U N T R Y " 9" © ORGANIZATION* | 9 © P O S I T I O N - . j I ! © ROYAL-COURT-POSITION I I ' ©GOVERNMENTAL-POSITION I 9 ©POSITION-HIERARCHY ; © ROYAL-COURT-HIERARCHY © GOVERNMENTAL-HIERACHY • © E V E N T 9 © D O C U M E N T * ©MUTUAL-DOCUMENT ! ©NON-MUTUAL-DOCUMENT * " © T I T L E Figure 4-14 Our ontology class hierarchy in Protege-2000 Within this figure the top left section (a) represents our top-level hierarchy which illustrates only the main concepts in our domain. The bottom left section of the figure (b) shows the TIME hierarchy in our ontology. Finally, the right part of the figure (c) demonstrates the break down of the hierarchy of concepts within our domain. Chapter 4. Build a history ontology 107 4.2.3.2 Assigning properties to classes (attributes & relations) Once we have our class hierarchy, we must assign properties to these concepts. In Protege-2000, these properties become slots attached to the classes. Slots can represent both attributes and relations associated to a class. A l l subclasses of a class inherit the slots of that class. For example, all the slots of the class P L A C E are inherited by subclasses of P L A C E . (Figure 4-15) fm N a s i * C ONTINENT [Concrete ( Name Ii RftHS^*ofre«mlrte* 1 SlRR-has-resldent* SI RR-was-born-here1 IlRR-died-here 1 JpA-name S] R-event-happened-at1 PI ACt (type<S IANOARD Ct ASS) I P L A C E ftole out itmentaUon Abstract* PLACE is an abstract superclass ivhich represents all related concepts to place. Name §J RR-has-resident1 ID RR-was-born-here1 gRR-dted-here 1 fpA-name SJ R-event-happened-at1 I Type J Cardinaliry Instance multiple Instance multiple Instance multiple String single Instance multiple C + Other Facets Classes=(RC-RESIDENCY-RELATIC. Classes=(RC.BIRTH-PLACE-RELXT. classes=(RC-DEATH-PLACE-RELA. classes={ EVENT) Type Cardinality Instance Instance Instance Instance String multiple multiple multiple multiple single Instance multiple C ' +| -Other Facets Classes=(RC-COUNTRY-SET) classes=(RC-RESIDENCY-RELATIC ciasses=(RC-BIRTB-PLACE-RElAT. Classes=(RC-DEATH-PLACE-RElA". classes=(EVENT) Figure 4-15 Inheritance of properties and relations by subclasses This figure shows the super-class "PLACE" and its subclass "CONTINENT". "CONTINENT" inherits all the slots attached to "PLACE". An attribute "name", defined as a type string, and a relation "happened-at" relates the concepts "PLACE" and "EVENT" for every sub-class of "PLACE". At this stage we used our list of attributes and relations defined in our concept dictionaries in conjunction with the conceptual model derived from the previous stage and attached the appropriate slots to the classes. This includes assigning attributes such as a string or a number value to slots and associating a class to other classes in the ontology by defining slots that represent relations. The remainder of this section explains how we defined relationships between the concepts in order to capture the dynamic temporal aspect of the history domain that we intend to represent. Chapter 4. Build a history ontology 108 The knowledge model of Protege-2000 conforms to that of O K B C [OKBC 1998], where slots attached to classes describe relations via a combination of binary concept-relationship-concept triplets. In other words, in Protege and O K B C , slots are nominally designed to represent binary relations. Slots also have facets, which specify the built-in constraints on attributes for slots such as value type, maximum and minimum values, cardinality, etc. Facets are a limited form of ternary relations. However, this framework does not facilitate attaching user-defined attributes to a slot (or relation). There are several possible solutions to work around this situation. The conventional method to model higher order relationships or to assign attributes to a relationship, in any K R system where slots are binary relations (i.e. at least any OKBC-compliant system), is to reify such relations as concepts (classes). In order to do so, we can create new classes with a structure that allows recording multiple concepts of multiple-arity relationships. This process is called reification and the resulting concepts are known as reified concepts or relations. Naturally, this solution also works if there is a need to have additional attributes assigned to the relationships. An example of this would be the following: o PERSON has-membership MEMBERSHIP o MEMBERSHIP has-interval TIME I N T E R V A L o MEMBERSHIP has-group GROUP OF PEOPLE o MEMEBRSHLP has-member PERSON When an instance of MEMBERSHIP is created, the participants in the MEMBERSHIP can be specified as well as the time value for that "relation". The lack of built-in support for higher order relations makes things such as visualization more cumbersome. In order to overcome this inconvenience, the Protege development group has introduced a couple of plug-ins. The " :RELATION" class is intended to be a tag class for reified relationships. This plug-in allows the user to view the reified relationship hierarchy in the same way that one can browse regular relations in Protege [Relation]. This feature is used in a couple of visualization plug-ins that simplify the visualization of instances of reified relations. This Chapter 4. Build a history ontology 109 is done by creating graphs which are connected with edges corresponding to the instances of reified relations. At the time of our implementation, the RELATION tab and associated visualization plug-ins were not available yet, thus we created reified relations as concepts in our domain and grouped them all under an abstract concept called "REIFIED RELATION" . In our design, we applied the reification for two main purposes. The first purpose is to assign attributes such as time to the relations that hold in our ontology. The second purpose is to implement temporal dynamic hierarchical structures such as our position and place hierarchy. Even though reification was an inconvenience for our former purpose, we would not be able to define the latter i f we could not encapsulate the triplet of concept-relationship-concept as a new reified concept. Figure 4-16 to Figure 4-25 illustrate the reified relations intended to capture the time element in a relation. For each reified relation, we present a figure which contains: a diagram illustrating the model designed for transforming the relation to a concept, the implementation of the new concept in protege, and an example of the instantiated reified relation. In order to reify a relation, we defined a new concept (class) with a triplet of slots: concept l-concept2-time. In addition to this, we captured any attribute associated with the concept or relations in this new reified class as well. 9 RC MEMBERSHIP-RELATION (type=:STANDARD CLASS) Name Documentation Constraints RC-MEMBERSHIP-RELATION Role Concrete This is a reified relationship. Entries here reflect tacts like 'Person Xwas a Member of group fat time range T1 toT2". Template Slots Name R-has-member1 R-has-time-range R-member-of! A-description Type Cardinalitv Other Facet Instance multiple Instance single Instance single String single classes={PERSON) classes={TIME INTERVAL) classes={SOCIAL-QROUP) PERSON (description) GROUP OF PEOPLE Figure 4-16 Reification of the relation MEMBERSHIP as a concept This figure illustrates the creation of a new concept MEMBERSHIP which represents the membership relation that holds between a "PERSON" and a "GROUP" in a time range (TIME Chapter 4. Build a history ontology 110 INTERVAL). It also captures the attribute "description" which provides extra information about any instances of the class MEMBERSHIP. The right part of the figure is our designed model, the left part of the figure is the transformation into Protege-2000. H4b) R has member : + R member of 1 V c + -R has start time | VI C j + 'p OrrtotogyVersion6_01505 Rhas duration V c + R has end-time <£> OntotoayVersion6_01509 Figure 4-17 An instance of the reified relation "MEMBERSHIP" This figure shows that two people: "Tabatabaie" and "Behbahani" (top left of figure) were the members of a group called "Koshandegan-Constitution" (window in the middle-right) for a certain time range (bottom left side of screen). ~ RC-RESIDENCY-RELATION (type=:STANDARD CLASS) Name Documentation Constraint^ RC-RESIDENCY-RELATION Role Concrete This is a reified relationship. Entries here reflect facts like 'Person X lives at Place Y at time range T1 to T2". Template Slots Name Type Cardinality Other Face1 SJ R-reside-in1 Instance single classes=(PLACE) JjjR-has-time-range Instance single classes={TlME INTERVAL) SjR-has-resident1 Instance single classes={PERSON) PERSON PLACE TIME INTERVAL Figure 4-18 Reification of the relation RESIDENCY as a concept This figure illustrates the model used to capture the "RESIDENCY" relation that holds between a "PERSON" and "PLACE" during a "TIME INTERVAL". The right part of the figure is our designed model, the left part of the figure is the transformation into Protege-2000. Chapter 4. Build a history ontology 111 R lias-resident i Mirza Hossein Khan R reside in i Istanbul R-has time interval IOmologyVersion6_01463 ME R has start time c + —~~J R has duration V SL +! R has end-time V c + ! -J i OntoloayVersior»6_ .01464 A n a m e Mirza Hossein Khan fcRRresidein C + I Ontotofly 6_00632 <|>Ontoiotiy-6_00707 fX 0titology-6_00926 V C c |x 1 Istanbul (type»CITY, name =Ontology-6_00633) Ik 3 > 1 Name RR consists of areas C + [Istanbul RR has resident V 1 C | + ) ~ RR belongs to city-set c + t Ontology 6_0O634 Figure 4-19 An instance of the reified relation RESIDENCY In this example, PERSON "Mirza Hossien Khan" (top right side of figure) was living in CITY "Istanbul" (bottom window) during a time interval (top left side of figure). As it can be noticed from this figure, for this instance we only knew the time of completion of the RESIDENCY relation, not the time it begun nor its duration. Chapter 4. Build a history ontology 112 § RC-BIRTH-PLACE RELATION (typB":STANDARD CLASS) [c Name Documentation Constraints RC-BIRTH-PLACE-RELATION Role This is a reified relationship. Entries here refect facts like 'Person Xwas born at Place Y at a time point T". Concrete Template Slots Name [ T y p e Cardinality Other Fa JSj R-was-born-here 1 JjJR-has-birth-place1 Sj R-has-time-point Instance Instance Instance single classes={PERSON) single classes=(PLACE) single classes=(DATE) (a) BIRTH-PLACE reified relation & RC-DEATH-PL ACE-RELATION (type=:STANDARD-CLASS) I_ Name Documentation Constraints RC-DEATH-PLACE-RELATION j This is a reified relationship. Entries here reflect facts like 'Person X died at Place Y at a time pointT'. Role Concrete • j Template Slots Name ! Type 1 Cardinality I Other F SJR-died-here1 Instance single classes=(PERSON) S3 R-has-time-point Instance single classes=(DATE) SiR-has-death-bed1 Instance single classes=fPLACE) 0>) DEATH-PLACE reified relation Figure 4-20 Reification of the relations BIRTH-PLACE and DEATH-PLACE as concepts The BIRTH-PLACE and DEATH-PLACE reified relations are presented as a triplet that consists of a PERSON, PLACE, and a TIME POINT in which the person was born or died. The right part of the figures are our designed models, the left part of the figures are the transformation into Protege-2000. Chapter 4. Build a history ontology 113 Rhas time point %• OntolotjyVer sion6 J 1 5 1 7 J c f e l g — _ X- OntotogyVersion6_0... -c > R has christian date V][ C I 1902 R has lunar date [ VJ| C + - J t 1319 R has solar date [ VJ( C I 1280 Figure 4-21 An instance of the reified relation DEATH-PLACE This figure illustrates an example of the DEATH-PLACE relation in our domain. In this example PERSON "Mirza Hossein Khan" (top left window) died in PROVINCE "Khorasan" (bottom of the figure) at a certain time point (top right window). An example for the BIRTH-PLACE reified relation would be identical to this one. c RCTITIE PERSON-RELATION<type=:STANDARD CLASS) Name Documentation Constraint d [RC-TITLE-PERSON-RELATION Role Concrete This is a reified relationship Entries here reflect facts like 'Person X had Title of honor Y at lime range T1 to T2". Template Slots Name J U L R-has-title-of-nonor1 Instance .5. R-has-time-range [SLR-is-nonored 1 Cardinality Other Fac single Instance single Instance single classes={TITLE) classes=(TIME INTERVAL} classes={PERSON} Figure 4-22 Reification of the relation TITLE-OF-HONOR as a concept The association of a TITLE to a PERSON for a time period is modeled through a reified relation presented as TITLE-OF-HONOR in this figure. The right part of the figure is our designed model, the left part of the figure is the transformation into Protege-2000. Chapter 4. Build a history ontology 114 T R-has-title-of-honor i Va^ir Azam 1 v cjHEE A name Vazir team RR is honored I.. J Vazir Azam R-is-honored Em O Dole V c Ein-O-Dole C x R has-time range V J C j + — i OntoloaWersionO 01601 > ___ . . . ^ | l.cj*f R-has-duration C + i R has end time c + : • R has start time +Ii -1 <|> Ont oloayVer s i . icui _u1 S01 Ein-0 Dole (I y.pe-PERSON. name-Ontotogy-6... I- ' In i jgf c > A name Kit has title of honor V | C f + l - ~j ll^Jffrtyaite Azam ] ^ Great Prince Atabak Figure 4-23 An instance of the reified relation TITLE-OF-HONOR This figure shows an instance of the reified relation TITLE-OF-HONOR in our domain. A PERSON "Ein-O-Dole" (bottom left) was honored with the TITLE "Vazir Azam" (window on the upper left) for a period of time (top right side of the figure). As it is obvious from this figure, we only knew the beginning of the time period in which he held the title, not the end date nor the duration. Name Documentation Constraint! RC-INVOLVMENT-RELATIONSHIF Role Concrete This is a reified relationship. Entries here reflect facts like "AgentXwas involved in EventYatj a time range T1 toT2 or at time point T. Template Slots Name ..] Type Cardinality s R-involved-in 1 Instance single s R-has-time-point Instance single s A-has-agent-role Symbol single s R-has-time-range Instance single s A-has-agent-status Symbol single s R-has-agent1 Instance single Other Facet classes={EVENT) classes={DATE) allowed-values=(leadBr,supportE| classes=(TIME INTERVAL) allows d-values=(.in-favor-of,in-cip classes=(AGENT) AGENT f agerrT^ ^status J TIME INTERVAL Figure 4-24 Reification of the relation INVOLVMENT as a concept The relation INVOLVEMENT is reified as a concept which consists of a PERSON, an EVENT, and the TIME POINT or TIME INTEVAL in which the involvement association is valid. The right part of the figure is our designed model, the left part of the figure is the transformation into Protege-2000 Chapter 4. Build a history ontology 115 R has agent V C f + X Mirza AM Asghar Khaiy C X A name Mirza Ali Asghar Khan RR-invoh/ed in X Ontoloay-6_00717 t Ontology 6_00785 |4>OntotoBy-6_00797 X Ontoloay-7_00973 S 3 A has agent status A has agent rote in-favor of spporter fx X j ft/srna R lids time point V I C I + 1 l / -Grantino Tobacco conceslon to England! <^ ftt<otonyV8r«ton6_01494| I J R R h a s agent C + i R precedence of V | C + / 1 Onto logy? Jibisb L^JOntolouy 7 ^00951J X^iSibacco Revolt 1 < I i R involved in v / c + -X> 12-Granting Tobacco conces ion to England R h a s - t i m e point <$> pntolouyVer sionfi _01494! R-has-time-range T Oi i to logyVersion6_ - 0 1 . . • I C l q | R has christian date c t i l -J I 1890 Rhas . lunar date i_y j _c t ±L -<$>1307 R has solar date I v c + (|-I 1268 Figure 4-25 An instance of the reified relation INVOLVEMENT In this example a PERSON "Mirza Ali Asghar Khan" (top left window) is involved in an EVENT " Granting Tobacco concession to England" (top right window) at a TIME POINT in "Christian year 1890" (bottom right window). Having explained how reified relations were handled, we proceed to explain the definition of our temporally dynamic hierarchy of places and positions. In our ontology, we defined different types of places (continent, country, province, city, area) which are interrelated. These interrelations (belongs to /is part of) are time dependent. In order to capture this dynamic temporal aspect of our hierarchy of places, we defined a set of reified relations as concepts. These include those concepts represented in Figure 4-26. The concepts in this figure are defined as SET concepts such as C O U N T R Y SET, PROVINCE SET, CITY SET, and A R E A SET. At any time point, the place hierarchy is conformed by sets of instances with different types of places. For these places, there is a part/whole (consist-of / belongs-to) relation Chapter 4. Build a history ontology U 6 that holds at each level of our place hierarchy. This means that any place class in the hierarchy consists of instances of the immediate lower level place class at any given time. In other words, the summation of every instance of the concept in the lower level will construct the concept in the higher level within the hierarchy at that certain time period. We used this feature to our advantage in our design and created our reified relations in a manner that captures the aforementioned characteristics. As an example of this, consider the class COUNTRY. We know that a country is located in a continent, moreover it consists of a set of provinces at any given time. As illustrated in Figure 4-27 and Figure 4-28, for each instance of the concept country we can capture two things that hold at a certain time: to which country set it belongs and which provinces it consists of. The country set to which this particular country belongs to forms a continent, again for a specific time interval. Figure 4-29 illustrates an example of the aforementioned association. In this figure, Country "Iran" is located in the continent "Asia" which at that particular point of time consists of the following countries: Iran, Osmani, and Russia. We should note that only those countries relevant to our domain were included in our ontology. At this same time point, the country Iran consists of a set of provinces: Espahan, Gilan, Khorasan, and Tehran. We used a "TIME I N T E R V A L " to capture the temporal aspect of this relation. In this case we only knew the time that the association between these places ended. Many of these times are unknown because they fall outside of the time range that our ontology intends to represent (the time range covered by our history book) Chapter 4. Build a history ontology 117 Figure 4-26 Modeling the temporal place hierarchical organization This figure illustrates the model we utilized to create a time-based hierarchy of places. As shown, there are five different types of places in our ontology: CONTINENT, COUNTRY, PROVINCE, CITY, and AREA. Each of these is conformed by a set of instances of another type of place (at a lower level in the place hierarchy). In order to capture the dynamicity of the place hierarchy, we defined a set of relations such as "located-in", "consist-of', "belongs-to", etc. between the places. These relations are all associated with time. Chapter 4. Build a history ontology 118 9> CONTINENT (type-:STANTJARD CLASS) Name JCONTINENT Documentat ion Name I .COUNTRY Role Concrete I Template Slotsii Role Concrete Template Slots Name I Type j. Cardinality |S] RR-consist-of-countries * Instance multiple ] R-event-happened-at1 Instance multiple • Name (CITY j Rote | Concrete j Rote M Concrete w ^ Name Type l]^nas^neTgnbor»^ Instance |pRR-coi\slst-ot-provinces1 instance 8] RR-beiongs-to-counttv-set1 Instance classes=|RC-COUNTRY-8ET) | classes=(EVENT) Cardinality Other Facets multiple classes=(COUNTRY) multiple ciasses=(RC-PROViNCE-SET) multiple ciasses=(RC-COUNTRy-SET) i template Slots ;.< ; Name ! Type . |MRR-consists-or-cities" Instance IBJ RR-belongs-to-province-set1 instance Template Slots < i _ Name Type.. §jRR-belonBS-to-cit!?i«» Instance |y RR-consists-oFareas1 Instance R-evenl-happened-at1 instance multiple multiple tlasses=(ROCITY-SET) classes=(RC-PROVINCE-SET) • template Slots : Name multiple classes=<RC-CITY-SET) multiple elasses=[RC-AREA-SET) multiple classes=4EVENT) ffl RR-belongs-to-area-set^ Instance [£s R-event-happened-at1 Instance RR-was-born-here • Instance Type I Cardinality j Other Facets multiple multiple multiple classes=(RC-AREA-SET) classes=( EVENT) classes={RC-eiRTH-PUCE-RELATION) M Figure 4-27 Class implementation of main place concepts in Protege R C - A R E A - S E T template Slots c RC-COUNTRY-SET (type- :S T ANOARD CLASS) jRC-PRQVINCE-SET © Rote Concrete Name R C - C F T Y - S E T | Template Slots Role (concrete Name IRC-COUNTRY-SET Documentation Template Slots N a m e • R-located-ln-ctmtinent' B R-has-country-set • SJ R-has-time-range Other I- at Name ER-has-prcivince-set * [J|j R-located-in-country1 OH R-has-time-range 1 Type Instance Instance Instance multiple single single Type I Cardinality Instance single classes=(CONTINENT) Instance multiple classes=(COUNTRY> Instance single classes={TIME INTERVAL) Olhet F-classes=(PROVINci') classes={COUNTRY) classes={TII«E INTERVAL) Template Slots ' Type j Ca id ina l ) t v „ R-tocated-in-province * Instance single RDR-has-clty-set11 Instance multiple Til R-has-time-range Instance single Other Fac! classes*! PROVINCE) classes^C(Tr) classes=tTIME INTERVAL) :r_l£J4MS*.. _j_ Type : ca rd ina l i t y j JR-has-area-set* Instance multiple ciasses=iAREA) j R-tocated-ln-city * Instance single classes=iCITY) j R-has-time-range Instance Figure 4-28 Reified relations used to represent the temporal dynamic organization of places in Protege Chapter 4. Build a history ontology 119 Name Iran l< IMS ntntjhiKM c + X Russia ' J Osmani i Ontology ?J)fJ486 R located-in continent V C\+ X Asia RR consist of provinces V c + -B P R has country-set Wtnm X Osmani "X Russia Rhas-time-interval V c •i- -I OiitalotryVersiotui 01463 R has duration C + ! Rhas-endtime V i Cj + i I OWologyversk)n8J)1464 X - Icjxj R-has-christian date vf C + -i 1872 R has lunar date vf C . - ; I 1288 Rhasst art-time CI + R has solar date I 1250 V C +l| - i R has province-set X Espahaii i>Gilan "f Khorasan 4> Tabriz <t> Tehran R-located-in-coiintry VJ C + <| Iran R has time interval V C 1 + <p OntotogyVer ston6 J ) 1463 Figure 4-29 An instance of the place hierarchy in Protege This figure illustrates that a COUNTRY Iran was located in the CONTINENT Asia (window in the top-middle), which at that time consists of Iran, Osmani, and Russia. The same COUNTRY Iran consists of a set of provinces (bottom-right window). All these relations hold for a time range which is represented by the concept TIME INTERVAL (two windows on the bottom left side of the figure). In a similar manner that we represented the temporally dynamic relations between places, we represent the governmental and royal court position hierarchies along with the people who hold these positions at any given time. We defined two reified relation as concepts: HOLDS-POSITION and POSITION HIERARCHY (Figure 4-30). The HOLDS-POSITION concept is created to represent the association between a PERSON and the POSITIONS that this person might hold at any given time. This reified concept also captures the inferior and superior of each position in a similar manner (person, place, time). The POSITION-HIERARCHY concept aims to represent the hierarchical structure of positions in an organization which, in our domain, refers to either a governmental or a royal court organization. Figure 4-30 explains our conceptual model associating both the POSITION-HIERARCHY and HOLDS-POSITION reified concepts. The HOLD-Chapter 4. Build a history ontology 120 POSITION relation is associated to the POSITION-HIERARCHY through a "belongs-to position hierarchy" relation. This encompasses all the people that hold a position in that hierarchy along with how these positions were related to other positions in the hierarchy at that time. We should note that, all these relations are time based and are thus associated with a time interval. Figure 4-31 shows how we utilize Protege-2000 to implement this hierarchy. An instance of this dynamic hierarchy is illustrated in Figure 4-32. In this figure, the position "king" was held by a "PERSON" called "Mozafaredin Shah" for a time interval (TIME INTERVAL). In this figure we can also see how the inferiors and superiors of that person in that specific time period are captured. REIFIED POSITION HIERARCHY RELATION *\ r position hierarchy POSITION REIFIED HOLDS POSITION RELATION reified holds position TIME INTERVAL PERSON Figure 4-30 Reified relations used to capture the dynamicity of the POSITION hierarchy Chapter 4. Build a history ontology 121 S POSITION (type .STANDARD CLASS) Name Documentation [ P O S I T I O N -- . p. Constraints i V i C Hate j Concrete Template Slots S Name SjA-PositJon-level A-name Type Cardinality OtherFac Integer required single minimum=0 String single RR-posttiorr-riolder1 Instance multiple _ - J J - ^ J ^ s e s ' j g ^ = RC HOLDS .POSITION-RELATION (type] Name Document pC -N^S_P0s l l10 l»RELATio7 Role C o n c r e t e This is a Entries hW 'Person % range T1 9 POSITION -HIERARCHY (type»:STANDARD CLASS) ->( — Documentation Constraints : V C POSITION-HIERARCHY Concrete Template Slots N-nrne ..Type jCardjnalityj Ij R-position-set Instance multiple iS, R-has-tlme-lnterval Instance single JjR-positlon-hotder-set1 instance multiple Other I classes={POSrriON) classes^fTlME INTERVAL) C lasses={RC-HOLDS_POSmON-RELATION) Template Slots Name RR-posltion-lnferior« R-holds-position1 RR-posltjorvsuperior1 R-belongs-to-position-hierarc. R-posltlon-holder" R-has-tlme-interval dina^r Instance multiple Instance single Instance multiple .Instance multiple Instance single Instance single Other facets ciasies^RC-H0LOS_P08lTION-RELATION) classes={POSITION) ,tlass8S=(RC-H0L0S PQSfflON-RELATION) fflas^jPOJfflai^RARcl^ cTasses={PERSON) classes=(TIME INTERVAL) Figure 4-31 Implementation of reified relations for position in Protege-2000 In this figure the three main concepts relating to position are illustrated: POSITION, POSITION-HIERARCHY, AND HOLDS-POSITION. It also demonstrates how we defined relations used to associate these concepts. Chapter 4. Build a history ontology 122 i Prime kt>Kino I Gilan Governor i Prime Minister I Prime Minister 1 f oi sign Minister % Foreign Minister } X> Khorasan Governor ' Prime Minister I Prime Minister |7 King Figure 4-32 An instance of the reified relation POSITION-HIERARCHY and HOLDS-POSITION in Protege-2000 This figure illustrates an instance of the position hierarchy that holds for a specific time interval in our domain. In this example, the position "king" (top right window) was held by a person called "Mozafaredin Shah" (bottom right window) at that time interval. We can also see the inferiors and superiors of that person in that specific time period (within the bottom right window). 4.2.3.3 Defining Constraints The next step in our formal ontology development is to specify constraints on the properties (slots) of the classes we defined. We do this, in order to ensure the consistency of our ontology. This includes defining constraints on both attributes and relations that these classes represent. We used built-in facets provided in Protege to assign constraints on slot values. Amongst the facets we used are: cardinality of a slot (how many values the slot can have), restrictions on the value type of the slot (for example, integer, string, instance of a class), minimum and maximum values for a numeric slot, etc (Section 3.1.2.4.2). In addition to these facets, we used P A L axioms to define more complex user-Chapter 4. Build a history ontology 123 specified constraints than those possible with facets (Section 3.1.2.4.2). The P A L axioms are used specifically for consistency checking of the temporal aspect of our ontology. Amongst the things we checked by using these axioms is whether any instance of the relations that associate two concepts, have discordances in their time attributes. For example, we must ensure that for any person the birth-date precede the death-date. These axioms were also used to check for the existence of loops within the ontology. As an example of possible loops in our ontology, we could have a case in the position hierarchy, where person A is at the same time a superior and an inferior of person B. 4.2.4 Ontology Evaluation After designing, building, formalizing our ontology using Protege and enforcing constraints on attributes and relations, we used the knowledge acquisition forms provided in Protege to instantiate our history ontology. Over seven hundred and fifty (750) instances were extracted from the history book and included in our ontology. Amongst these instances we find: people, places, documents, events, etc. Before we started using the ontology, we needed to evaluate the model as a whole to examine whether it satisfied the previously specified motivating scenarios and whether it provided answers to all the competency questions we designed it for. In order to test each competency question or motivating scenario we employed one or more of the following choices provided by Protege: • Using the built-in query engine to provide answers for simple queries. (Figure 4-33) Our implementation allows us to answers those competency questions that are directly related to instances of concepts by using the built-in query engine. In Figure 4-33 we looked for instances of people who held the position "king". • Using the P A L query plug-in to create more sophisticated queries. (Figure 4-34). We addressed those competency questions which could not be answered using the built-in query engine by posing them using the P A L query plug-in. This plug-in allows us to make more complex searches like the example presented in Figure 4-34. In this example we search for places where one or more events took place. Chapter 4. Build a history ontology 124 Using visualization facilities provided by Protege plug-ins in order to browse the ontology to ensure that our representation is accurate and consistent. Figure 4-35 and Figure 4-36 show two of the different available visualization plug-ins in Protege-2000. In these two figures the place hierarchy related to country Iran is presented. Visualization aids are particularly helpful when trying to understand hierarchical relations. Prma Window IMp PAL CMMttrsMs I UVu I ati CJ I* tt % ft ions Qmtrm : KnowliKJae Un I'At Outruu c i Instance tree « ttPtttBbfttv? TOVuT«b © Jamtwtaya XML * • * 8» Stet* . f - «<K* I Instance* 4\Ouores Knawitdg* AcquKlttoii < J;: CLxvcs&Wtstansts PAt Constraint* . ~ j J ^ t * l t a * i * « « J V i £ as* V + - w : V * I King tRv-H«.D3_POS:l lON-REI <Mfl PC-HOLDS.POSSTION-REI More Cttw 6 w io v»«ie the u n s i - 5 <*how tft* tin *t orr*i?>n. L asnion. am 1 ft WHO v>« rt II it K n $ t f <sttO»» t i t ptrtM « *» MNC S»» p»Mc4 [3$ *tf*ms I hne Mvthrt in? (shower*tt.altlif:vc•/*-»)**(tvtnt, |H> M M t a lung ttvototd in? (sti<Mvt«t tvanht >Q attMNMiirl ft : » II ry mmnl "NuiWyirtg » « l o t mo tK «M «' »'• apr<«"*it a l * all MMM ihst kapatntdat#«HTO ptaw as. even *M»^ iin>n •pn» ] ImehMMM itUfton {tootavj tw »v»io W W H i t i M t l M M » an M M f I M I M M M <»*>«**» * * M H t m Wrvofc* in Wt M M tomt mm i 1 > M M f/tnts mat M»»t«M at t o ' T t w r i ' Owi* (typ»-RC Arjtt to 0**fAfer«ry Mfi<* . i ... ... v c * -X UCMUftfrn Snail H ix i j . l s | , iSliiitfl : V c + -K m - ran W W V c • j O n i u l u < j rV « 8 . i !K i6J ) i S3 ' « M»s«tt<im sh»h V C +1 -I King ti li t i t»s*> rami* V C • * Figure 4-33 Using Protege-2000 built-in query engine to answer competency questions In this example we answer the question "Who were the kings?" using the Protege-2000 built-in query engine. Our model returns two instances of the triplet "person, position, and time" (in the outlined windows). In this case "Mozafaredin Shah" and "Naseredin Shah" held the position "KING" at different time intervals. The bottom left part of this figure shows a few of the questions that our ontology is designed to answer. Chapter 4. Build a history ontology 125 Project Window H e * TGVwTa* PH. Constraints Relations © Jenibaieya P A L Constraints * i • Classes 4 Instances X M L P A L Gutties Cfi tow r v Instance Tree lOVutatt *"•* Kiwuuiedae free •- Classes , S Slots Fa rms i:: Instances ' M l Queries , Knowledge Acquis i t ion tZPmtbfWZ thoose Quer ies y v v c + - x Evaluate' Status Q u e i f : ?ptac# =* *«n K, i *v*nt i» i f * t T i h t . l ' W a r n about Indicated quel ies Evaluate Indicated quer ies 1 fc.rpoe I >"ijuV •*-».rn Di-w.it plar«. {type PAi Q U f R Y , rwms-Ontotogr ?_01?58) PTBIRI x : * j ^ n >' J T«hi« _ _ r. :; x . imcnir -X Kerman qpvtni X y<t*hh4ri event-elect •« that at least a n t event happened in mem * >vi ! It-,' • -•PAL STATEMENT * P AL • RA lirjF •Ti'daii 'p iste Smteni i uf ^-frv»r*e_or_hepptfie«-«r ? piece) •MMQi t (tiunange 'place :f RAME PLACE) ,; ( d » * « m r » tn-tnt f RAMS EVE NT) If i i. 1 1 1 l'rpi!*r;,-;t<e in Iran* None wJ 1 II ; Figure 4-34 Using the PAL query engine to answer competency questions In this example we look for places where at least one event has happened. The pop-up window (window in the middle of the screen) illustrates the PAL query statement written for this search. The result for this search (right side of screen) is a list of places where one or more events had taken place. If we select any of these instances, detailed information about that particular place is presented. Chapter 4. Build a history ontology 126 urn* mmiMM. 1i.„ mmi\ u. ..uimiw ~ JK\. !'!/i/.l' .itill Untolaf^uiniologyVaisiont 3. poi j l V"ma Window Help »>*l Canstrwnis lGV«t*t> • Relations OnlouiJ!: i . nw«ttt«te tree PALQuerfts Instance Tree OPallafc Rev2 TCVttlat) © Jambalaya XML Classes ' s Sals " " f o r m * i instances 44 Queries Knottledpi AoujuiMioo Classes & Instances Select tapitvn nstanc* ^ I Um • IIl*W-»^i>g8-to-?<wnlrY<-sel f Hfift-ha* tamer t* ©- * Iran •> >$ 0$tte*» I R»«s>a 9 [f3 )Wotal«C-ifi<ar*«iH *> <X'A»8 [H R -bss tum- range o- 4:. eitfetajr ;_c u* ? ••[|Hft-h»#-ne*jNi» Hjft-I* Knit— 1 * • Ha>4jiMMHMMMky ^ ISlfrMt-aMniKe-Mt o i Etaahsn #• X M M O- 1 l l . a r .Ja l , f » • TafciS «• I m.ran j v a K l * • I k t iC i iKi i an &• i r»* f iSlR-h*«-l»M-r*r»e* • • -|» O««aM«w<*ienT_0i SOS R h a s - i x w M . * . I FT |. jhart •X 0>»V| >)! TabM • i T«*an •t Kei-»i»n i|> va*l ti> M N M I M M . . :fi* N touted It IMK c h m l l , ™ <1, R-iws.huwr date x iiS tt has solar riace <* an R-haschr it h a * sow date V C • ! - ! V C • ! -I V C +i-I V C N-has i v c •! -t X CilOK3iV»-Si6n6_OI 501 R-tia«-st»Mfa* V X- OHK*3JVI»*IW?_UI S>M Figure 4-35 "Knowledge Tree" visualization of the place hierarchy for "Iran" In this example we utilized the "Knowledge Tree" visualization Tab plug-in to demonstrate the hierarchy of places related to "Iran". On the left side of screen we can see all the notions that relate to country "Iran". Amongst these notions we may find the country set to which it belongs (Iran, Osmani, and Russia), the provinces it consists of (Espahan, Gilan, Khorasan, Tabriz, Tehran, Kerman, Yazd, Mazandaran, Fars), and the continent it is located in (Asia). All of these relations for a given time range (windows in the right side of screen). This visualization plug-in allows us to brows through all this information in a single screen. Chapter 4. Build a history ontology 127 S?j — •• l'iutet.1 W i n d o w tine I 'AL cansiiMiit I G V u U t i C ^ 0 % » : K « * « t . o n » O n t o w r I K n o w t e d f l E I r e * I 'Ai a m i e s C 3 i int .wi f *• Ire*- ( • / l»aJ Ia t>Ho«z ! « V I * t * t o © J a n t t i a M u a X M I c C l a s s e s s S l o t s " f o r m s I i n s t a n c e s M Q l t t t t M M n t M e t i g e Aci|ui«tK>tt c i , : C l a s s e s A M s t a n c e s P * l . ( : I M f t i i 3 trnmiil "" tram* » n a n v C: ill X C " •* M M ! 'CM eFOUMMN CU iCONIMEMf C pftCvilCE 01) •Herein* 0i f A W ft? c COUNTRY*1 (D I «MMt* c K F * 1 S O N M <b4> M v c .-J y m taffem* 1 # r i a n t * : Iran !T f a n rfe OcajtM $ n u t t t a M Oo»itsU»»t>r««>!*_015... ff lUiavmtiiiHsv I V C I i V C l WLWLf I v c '"V: U 0«!»*>ih,''»«<Xt»_8l Figure 4-36 Using TGViz visualization tab to browse the hierarchy of places related to country "Iran" In this example, the hierarchy of places related to country "Iran" is presented in a graphical manner where every node in the graph represents a class or instance and the lines connecting them denote a relation. By selecting any of these nodes additional information related to that particular node is presented. In this example we selected the notion time interval (outlined) and the information about that particular node is presented in pop-up windows (right side of screen). In this case the relations represented by the graph hold from year 1849 to 1879 in the Christian calendar. We ran an exhaustive set of queries to ensure that the system provided satisfactory answers to all the competency questions and adequate, useful solutions to all motivating scenarios. Our testing yielded satisfactory results. We were able to provide adequate answers to each and every competency question we had designed our system to answer. In addition to this, the system provided facilities to support the requirements we had imposed on it with our motivating scenarios as well. As an example of this exhaustive set of queries, the following section describes how our implementation provided an answer to the competency questions stated in Table 4 -5 . For clarity purposes, we performed the set of queries for a particular PERSON "Mirza Chapter 4. Build a history ontology 128 Hossein Khan" and a particular GROUP of people "Koshandegan". To avoid repetitiveness, for the cases where two or more questions were similar, only one question was answered. As stated before we should note that Protege-2000 is a frame-based system and as such, it can provide results and answers to queries with a granularity level of a concept (class). Therefore, the output of a query is a frame that represents a concept. In order to browse the properties (detail) of this concept, we have to select the specific concept amongst the results and its full details are presented by Protege-2000. The following is the list of questions taken from Table 4-1. For every question, we present a corresponding figure showing the results obtained from querying our model in Protege. Question 1: Who was "Mirza Hossein Khan"? Question 2: WhereAVhen was "Mirza Hossein Khan" born/died/reside? Question 3: What title of honor he held and for how long? Question 4: What positions did he hold and for how long? Question 5: Who was the superior for each position that he held? Question 6: How was the position hierarchy organized at that time? Question 7: What documents did he make? Question 8: In what events was he involved? Question 9: Who else lived at the same era? Question 10: Who were the members of group "Koshandegan-(Abdol-Azim refuge)"? Chapter 4. Build a history ontology 129 Project Window Help PAL Constraints i i i i i Instance Tine © Jamtoalaya PAI Queries EZPaiTah Rev2 PAL Constraints S Slots I forms: • msrances rt Queries Knowledge Acquisition Query Class V + - Slot | V • li String c PERSON* (SjA-name lis jMlrza Hossein Khan More Clear 1 "Find i i Classes fc Instances ^SearchResults(1) j V | 4> i-Mirza Hossein Khan (PERSON) QuayiMame_ Who was "Mirza Hi Query Library <<4 Who was "Mirza Hossein Khan" ? i Q Where; When was "Mirza Hossein Khan" bom? ©Where/ When was "Mir/a Hossein Khan" died? >4What title of honor dM he hoM and for how tang? / Add to Query Library Mirza Hossein Khan (type-PERSON, name-Ontology 6 00 602) •name A-has-oender ]Mina Hossein Khan A desci lotion Brza Hossein Khan (Sepah 8alar) was a knowiedgabie and reasonable man. He was Irving for a while in Istanbul and other places and knew how European countries were ruled. Wien he appointed to be Ihe Prime Minister, he triad to organize the goverment Therefore he originated the Ministreiies in a same manner as European ministries in Iran There were one Prime Minister and nine ministries as follows: min. t l i . , Intain" mtn.vtr., Pnfr.i . Male RR-has4ille-of.honof c + f? SefiahSatar -1 Vazlr Azam A-lias-nationality I Iranian Figure 4-37 Results for Competency Question #1 Question 1: Who is "Mirza Hossein Khan"? This figure represents a query search for the person called "Mirza Hossein Khan ". The top left side of the main window illustrates the query statement. We are looking for an instance of class PERSON whose value in slot "A-name" is equal to "Mirza Hossein Khan". The right pane illustrates the results for this search. The results show we found a person with that particular name. By selecting that instance "Mirza Hossein Khan", a pop-up window appears. This window includes all the properties of the instance of class person "Mirza Hossein Khan". The user is then able to navigate through the information provided. Here we demonstrate the description field which gives an overview of the biography of the person. Chapter 4. Bu i ld a history ontology 130 Project Window Help PAL Constraints 0 " " > V K ' _ i Instance tree © Jamlialaya PAL Queries EH'aHali nm! PAL Constraints i Slots [ - f i r m s ::. Instances MQueries KnowledgeAcqwsmon Classes & Instances Query Class | V | + - slot V + " V i +1 -I Dfj ©RC-aRTH-PtACE-RaATIu gl Rwas-bornhere contains w : & Who was "Mirza Hossein.: I hislory_01 <M4 . "J3E p i l l | More ^ • i Clear j Find j Query Name R-was-born-here V C + | -| Iwhere/When was "Mirza Hossein Khan" born? I Mn to Hossein Khan Add to Query Library Query Library R has birth-place |v] cj V X « | Who was "Mirza Hossein Khan" 7 Where) When was "Mir hallos sem Khan" bom? Where/When was "Mli ia Hossein Khan" died? '- What lute ot honor did lie hold and tor how lona.? I Khorasan R has time point j . C ; * 1 JSearcnResults(1) V SS\ i history 01644 (HC IIIttlH PI AC Figure 4-38 Results for Competency Question #2 Question 2: Where/When was "Mirza Hossein Khan" born? This figure presents the query where we are looking for Mirza Hossein Khan's "BIRTH-PLACE" and "BIRTH-DATE". The result is shown in the right side pane. By selecting this instance we can observe that PERSON "Mirza Hossein Khan " was born in PROVINCE "Khorasan" and his birth date is unknown (window in the middle). The query process and results for capturing residency and death place are similar to this example. Chapter 4. Build a history ontology 131 9 Project Window Help PAL Constraints _ _ _ @ i WW i Knowledge tree Ontovlz i Classes S Slots Ouery jClass | V | •[ —) Stat |_V c FtC-ilTU-l>ERSON-RE_U .[§] R-is-honored Query Name iWhat title of honor did he hold and for how long? Query Library SiWIw was TMIiza Hossein l<han"? |§S Where/Wlien was "Mirza Hossein Khan" born? f<t Where/When was "Mirza Hossein Khan" died? f§- What in le of honor did he hold and for how long? Instance rise © Jainliaiaya PAI laioiies foims i:: Instances M Queries t/PailabRev/ PAL i onsliauiis Knowledge Acquisilloii Classes & Instances Search Results (2) contains V + - Q # Who was "Mirza Hossein.. | R has -time range I V1 C i i OntoiogyVeisionij j j i4«4 | Rhas title of honor | I SepatiSalar | R is honor ed i|> Mirza Hossein Khan r. > • ii - ! > Add to Ouery Library i Vazlr Azam I R C itiLt P E R S O N I-SepahSatar ( R C - T I T L E - W R S O N ' VazirAzam (type-R.. : : c 1 ycJS alias-duration V C ! R has time range C +1 -i R-has-end-time V C | Rhas title of honor VI C j + f - i X> Onlolo_rVersion6_01486 i Va/n Azam R has start time V C | R-is-honored V l Cj +1 -1 X OntologyVersion8_01484 ! i Mirza Hossein Khan Figure 4-39 Results for Competency Question #3 Question 3: What title of honor did "Mirza Hossein Khan" hold and for how long? In this query we look for the titles of honor that "Mirza Hossein Khan" held and the duration that those titles had. Two instance of title of honor belonging to "Mirza Hossein Khan" were found (right side pane). The pop-up windows in the figure show the information included in these instances (title of honor, name of person who held it and the duration). As it can be noticed for the title "Vazir Azam" our model does not contain the exact time interval that this title was held. However, for the title "Sepah Salar" we could find this duration. Chapter 4. Build a history ontology 132 S? , . , . , „ . . . • . . 2000%fe« ar y.npr|) Pro)ec« Window Help PA l ConstraWs HHS SMI r Knowledge 1 roe Ontowz : t Instance Iree © Jambalaya PAL Quel ies EZPalTab RevZ PAL Constraints Classes S Slots Foims i:: Instances ' M Queries Knowledge Acquisition t r. Classes & Instances Query Class i V | +1 - 1 Slot jVJ|*f"~1 ] w j + 1 - 1 o jsearch Results (6) V i> i Prime Minister (RC HOLDS^PO! •E,l*CHrXDSjrosiTION«^ (contains - r j Q Who was "Mirza Hosseinl 1 i Gilan Governor (RC-HOLDS PO! I Prime Minister (RC HOLDS _PO j«S> ForeignMinister (RCHOL0S_P( I Khorasan Governor (RCHOLDS I Justice Minister (RC HOLDS _P< Ware clear J r i i Mill! n i i i i i w i l iype... L J h " " 1 L >, Find Query Name What posit ions did "Mirza Hosse in Khan" hold (and tor how long)? Rholrts-posltion V C + -d> Prime Minister Library QueryLlbrary R position holder V C • - X j i^tMio was "Mirza Hossein Khan" ? H Where/ When was "Mirza Hossein Khan" born? iCf Where; When was "Mirza Hossein Khan" died? i® What title of honor did he hold and for how long? |& What positions did "Mirza Hossein Khan" how (and for how long)?! i Mirza Hossein Khan It has lime range V C + -I OutolouyVersioiHi U14H4 « j J T i Figure 4-40 Results for Competency Question #4 Question 4: What positions did "Mirza Hossein Khan" hold and for how long? This figure illustrates the results of the query in the right side pane. It can be seen that this person held six positions throughout time. As an instance of these results the pop-up window in the middle shows that the position PRIME MINISTER was held for a particular time interval by "Mirza Hossein Khan". Chapter 4. Build a history ontology 133 Project Window Help PAL Constraints Query J Instance hee © JamUalaya PAL Queries tZPalTali Rev2 PAL Constraints -Forms i:r Instances *HQuer«s Knowledge Acquisition ,,: Classes & Instances •[Class V + - Slot "I v l * jpT ' V + -" Qjl c r«-ltOLDS_iH)SITIC*|.RE... SJIW.|iosltion4nferior j contains • a Wltat positions did "Mirz_. i 1 1 Mote , 'i Clear : Find Query Name Who was Ihe superior of "Mirza Hossein Khan- for each position that ne held? | Add to Query Library — •asmr-n 4> K i , w i i v u e « R C HOI I S POSITION P H ATIOH.Ffi¥W>Mi 4 Kins (FtC NOLDS_POSITION V Prime Minister (RC HOLDS i Native Minister (RC HOLDS r Nairve Minister (RC HOLDS R holds position KinB | v c Query Library If Who was" "Mirza I' •O where/when war 10 Where/When war pwhat title of Nana 1 Ot What positions die! _ r. , :r—•-. Q W h o a r e t h 8 s i i W | R ^ s * l o n * o l a w I.YjJCj <$ Naseredln Shah RR-positlon-inferiot V C I Prime MWster i Prime Minister K|> Prime Minister i i Prime Minister K belongs to position-hierarchy i Ontolor_<ijljb611 Prime Minister (type-RC HOLDS_POSITtON RELATION GOVERNMENT... V c + -ft holds posit run i Prima Minister R position holder [yj[c£+j 1 MM 16 Hossein Khan RR position inferior V C j3> Foreign Minister It belongs to position liter aicliy _________ R has tirnerange I OntologyVerslor>6_01464 RR position superior _ _ , . . . v i e I Figure 4-41 Results for Competency Question #5 Question 5: Who was the superior of "Mirza Hossein Khan" for each position that he held? This figure illustrates the results for the query looking for people who were the superior to "Mirza Hossein Khan" for each position that he held (top-right pane). As a particular example the two pop-up windows in the middle show that king "Nasseredin Shah" was superior to Prime Minister "Mirza Hossein Khan" at a certain time interval. It also demonstrates that these two positions belong to the same position hierarchy "ontolog_6_00611". This hierarchy will be explored in the next figure. Chapter 4. Build a history ontology 134 (cT) GOVERNMENTAL-HIERACHY Instance^Tree <?- <£> Ontology-6_D0611 [SO R-positiDn-set e - <|> King <s** <$> Prime Minister ©- <•!> Trade Minister ©- <j> Profit Minister ©- <$> Justice Minister 9 - <j> Duty Minister ©- <f> war Minister <j> Foreign Minister ©- ^ 'Nat ive Minister e>- -C$- Science Minister ©- <£* Royal Court Minister ®- <£• Ambassador <|> Gilan Governor -tSil R-has-time-range 9 <|> OntologyVersion6_01 4B4 I [Sj R-has-end-time <p [SJ R-has-start-time 9 X OntologyVcrsionB_Dl 464 <j> [Si R-has-christian-date j <5>- at-1872 5 9 Is! R-hars-lunar-datu (c5 GOVERNMENTAL-HIERACHY Instance Tree 9 -t> OntolOBy-B_0QB11 i 9 "HI] R-position-set <£- King <? ];H3 RR-position-holder 9 <t> King I'S; RR-position-superior 9 S i R-position-holder ©-<$> Naseredin Shah 9 L§] R-has-time-range 9- OntologyVersion7_Q1 5B6 9 | S i R-has-end-time <|> OntologyVersion6_01 501 9 |S] R-has-christian-date <b--^ > 1879 9 [is] R-has-lunar-date ©--'JC-1313 9 EM] R-has-solar-date ©- <J> 1 276 ©- | 'S: R-has-Start-time [S] R-has-duration ©- [sl RR-position-inferior ©- fs] R-holds-posltion O- fsl R-belpngs-to-position-hierarchv .<c) GOVERNMENTAL-HIERACHY iiiiifllfs;>>^^ Instance I too v ' C i 9 Ontolctgy-BJDDB11 I 9 LSj R-position-set ©- <$> King 9 ?• Prime Minister 9 [ § ] RR-position-holder 9 ••••$> Prime Minister j ®" l.S.I RR-position-superior | 9 R-position-holder [ G>-<f> Mirza Hosse in Khan 9- L§3 R-has-time-range 9 <£• OntologyVersion6...0i 4B4 9 iSJ R-has-end-time 9 <fc> OntologyVersion6_01 480 9 [S] R-has-christian-date ©- <t'1B74 9- Dsl R-has-lunar-date ®" [s] R-has-solar-date Tsl R-has-sta rt-time 9-<j> qntologyVersion6_Q1 464 9 LS) R-has-christian-date <£>-1872 ©- [S] R-has-lunar-date ©- [s] R-has-solar-date i c) GOVERNMENTAL-HIERACHY Instance Tree 9 Ontology-6_0QB11 ®" [Si R-position-set 9" [ § ] R-has-time-range 9 tSl R-PDSition-holder-set ©- <$> PrimB Minister 9- -i> King ©- <|> eilan Governor ©- <£> Prime Minister © - <$> prime Minister 9- <$> Foreign Minister ©- <£> Foreign Minister ©- ^ Khorasan Governor ©- Prime Minister <b- <£•• Prime Minister ©- £ King s>- <£• Justice Minister ©- Ambassador ©- Prime Minister ©- <J> Ontology-6_0D819 G>- <f> Ontology-B_Q0827 Figure 4-42 Results for Competency Question #6 Question 6: How was the position hierarchy organized at this time? This figure illustrates the organization of the position hierarchy at the time that "Mirza Hossein Khan" held the position "Prime Minister". Instance tree (a) shows the hierarchy of positions starting at year 1872. This hierarchy is organized based on the importance of the positions. Every position has a ranking specified by a tag (not shown in this figure). Instance tree (b) illustrates one of the instances of position "king" which was held by "Nasseredin Shad" who at that time was the superior of "Mirza Hossein Khan" when he was the Prime minister. As it can be noticed he became the king in 1879 which means that another person held this position before him. Instance tree (c) shows the time during which "Mirza Hossein Khan" held the position of Prime Minister (1872-1874). There are other people who held this position after him. Instance tree (d) demonstrates all the positions that were assigned during the time that this hierarchy was valid. For example the position "Prime Minster" has been assigned to 5 people during this time. During this same time range, there were two kings. Chapter 4. Build a history ontology 135 9 Project Window Help PAL Constraints • »• a % % r: Knowledge Tree Oniovu • i instance Tree © Jambalaya PALOueries H KPallab Rev2 PAL Constraints c Classes M Slots iuntts Instances ( J | Queries Knowledge Acquisition Classes & Instances Query • , Search Results (1) V! £rl Class ! V \ + II - i Slot V + ~ j VI + t ~ : | 1 Tobacco concession (CONTRACT) c DOCUMENT* SRmade-by 'contains ^ I # Who was "Mirza Hossi \ 1 1 Tobacco concession (type-CONTRACT, name-Ontotogy-6_00739) . • I J ^ f c k A document-title A content More:, j Clear JTobacco concession in 1268 Naseredin Shah gave the Tobacco QueryNarne koncession to England According to this o^nttact Ihe license of selling Iran's jobacco both in Iran and outside Iran had jwhal documents he made? R-has-publisb date V C + -I OntotogyVetsiona. 01494 been given to an English man. Query Library from the spring ot 1370(1308) the Employees of the brfBsh company started to work in Iran Iranian and the merchants announced their disagreement and the Tobacco revolt btarted RltMio was "Mirza Hossein Khan" ? PWiere/When was "Mirza Hossein Khan" born? >Q:Where/When was "Mirza Hossein Khan" died? R•made by C • t Mirza Hossein Khan 'v What title of honor did he hold and for how long? j 0 What positions did "Mirza Hossein Khan" hold (and fori p§!in»io are the superior of "Mirza Hossein Khan" tor eatj I NaseiedinShah I England I _ _ . I I f s s s a j M a M t H M ... : :.:::!: : :.:..::: i ; : .... . . M: ' ' ' s • Figure 4-43 Results for Competency Question #7 Question 7: What documents did he make? This figure illustrates the results obtained from query for the documents made by "Mirza Hossein Khan". The right side pane shows the only document made by him. The type of the document is a contract and we also can find out the time when it was written and the other agents (people, groups or countries) who were involved in creating this document in the pop-up window. Chapter 4. Build a history ontology 136 _ history Prolege*-2000 (C:\Progrem Flles\Protege -OOOUiislorypprj) Project Window Help PAL Constraints - a y instance Iree © Jamlialaya PAL (tomes M EZPalTab Rev2 PAL Constraints • instances ! Mi Queues Knowledge A< gu,sru,,u Classes & instates J [Search Results (8) V Query Class V + - Slot ! .vj_l -J v l . _ j - j (&RC.«v_\/_Nr4_AT_. g Rhas- -tjeni 1 1— contains " 1 Q Who was "Mirza Host 1 '« — _ _ _ _ _ — • • ., - . . . ; .1 Moie Clear Fmtl GnervName In what events was he involved Add lo Query Library Query Library -;,;,.„„;,___•._. ;„;,„;,;,_._„._. V X • Who was Kara Hossein Khan" ? • Where/ When was "Mirza Hossein Khan" born? ft Where/ When was "Mirza Hossein Khan" died? § Wlial title of honor did he hold and lor how long? ft What positions did "Mirza Hossein Khan" hold (and for how long)? R|Who are the superior of "Mirza Hossein Khan" for each position that he held? '©What documents be made? O In what events was lie Involved <f*-flrst Travel To Europe li__iv_\l t 4 Deposing Sepah Salar (RC INVOIV I 5 Assigning Mirza Hossein as GHan C •1 8 Assigning Mirza Hossein Khan as I l> 7 Depose Mirza Hossein Khan from t I 8 appointing Mirza hossein Khan as t P 1 Summon Mirza Hossein Mian from S 7 Eslanlishaig Mniislries (RC INVOL Figure 4-44 Results for Competency Question #8 Question 8: In what events was he involved? The results of the search for the events where "Mirza Hossein Khan" participated are displayed in the right pane of this figure. By selecting any of the instances of the events listed, one can get additional information related to that particular event. This includes a brief description, people involved, time range, consequences, and documents related to that particular event. Chapter 4. Build a history ontology 137 ^ h f e , 0 7 P r o M g i 2 0 0 0 <C:*°rogram Ffles\Protege 2O00Uifeforj.pprj) Project Window Help PAL Constraints c J Instance Tree © JaiiiUalaya PAL Queries • . Foirns i • instances «Queues v • t .Query at the s a m e era a s ' M i r z a Hosse i r EZPalTaD Rev2 PAL Const! aims Knowledue Acquisition (Otteiy Responses Classes & Instances j Attachments for selected query / + -I Peopelwho lived at the same era as "Mirza Hossein Khan" (type.EZ, Name [Peoplriwhc^r^^ Description (findall ? P E R S O N 1 dnda l l V P E R S O N 2 (and (not (> OR-has-birth-date' ? P E R S 0 N 1 ) CR-has-deattvdate' ' P E R S O N 2 ) ) ) (not (» fR-has-birth-date' ? P E R 8 0 N 2 ) CR-has-death-date' ' P E R S O N 1 ) ) ) ) (and (subslnngof 'Mirza H o s s e i n K h a n ' f A - n a m e ' ? P E R S 0 N 1 ) ) ) » [This Query gives a list of people who live al p ie same time as "Mirza Hosse in Khan" [This is done by comparing the birth-date and death-date of all the Instance of | P E R S O N with birth-date and death-date of Mirza Hosse in Khan" Range ] (defrange ? P E R S O N 1 FRAME P E R S O N ) (derrange 7 P E R S O N 2 :FRAM£ P E R S O N ) 7 P E R 8 0 N 2 j .?PEgsgNi_ I Mirza Hossein iMtart P Mirza Hosse in Khan I Naseredm Shah I Miiza H o s s e i n Khan % Seid Sa leh Arab \ I' Mirza H o s s e i n Khan I Haj Mola All i Mtea Hosse in Khan i pnme Minister X I Mirza All Asghar Khan "1 $• Mirza Malkon khan Espahara -P Mirza H o s s e i n Khan P Mirza H o s s e i n Khan V Mirza Hosse in Khan S i e d J a m a l e d i n A s a d Abadi -Ha) Mirza Javad I Mirza Hosse in Khan V Mirza H o s s e i n Khan AghaNaja f i | I Mirza H o s s e i n Khan ••Mirza H a s s a n Ashtyani f • Mirza Mohamad Shi raz i . I< p Mi iza H o s s e i n Khan I Miiza H o s s e i n Khan Mozafaredin Shah f Mirza H o s s e i n khan > Miiza All Khan Sheykh Yahya Kashan j | % Mirza Hosse in Khan j - M i r z a Hosse in Khan • N o s e ti- Mirza H o s s e i n Khan > Tahatabaie N i Mirza H o s s e i n Khan fcehtiar.ar.i f Miiza Hosse in Khan 1 Sheikh barini ! C Mirza H o s s e i n Khan Haj Mirza Mohamad Reza ( > Mirza H o s s e i n Khan Zaftar-ol-Saltane & i Mirza H o s s e i n Khan Ashtiyanl % Mirza Hosse in Khan Ha) Sheykh Mohamad Vaez < Mirza H o s s e i n Khan Ai la-O-Dole — j < ' Haii 8e id H a s h e m Ghandi K • Hap S e i d E s m a i e l Khan V •Ha) Mirza Alinaghi P Mirza H o s s e i n Khan P Mirza Hosse in Khan : Miiza Hosse in Khan > Mires| H o s s e i n khan Ein-O-Dole « C Mirza H o s s e i n Khan ' Sheikh Mohsen khan Moshi < P Mirza H o s s e i n Khan • S ied H a s s a n K / M i r z a Mehdi Khan Vazir Hon < r Mirza Hosse in Khan > Miiza Hosse in khan Figure 4-45 Results for Competency Question #9 Question 9: Who else lived at the same era as "Mirza Hossein Khan"? This figure illustrates the use of the PAL QUERY engine in Protege-2000 to search for of instances of people who lived in the same era as Mirza Hossein Khan. In order to do this we compare the birth-date and death-date of this person with every other person in the domain. The outlined window in the middle shows our PAL Query statement and the right side pane demonstrates the results obtained with this search. This query could be extended and refined to only include those persons in a specific area or with a specific relation to Mirza Hossein Khan. Chapter 4. Build a history ontology 138 s» l i ~~~ ; ; — Protect Window Help PAL Constraints (Hlj i Knowledge tree Omovlz . : tnslance Tree © Jambalaya PAL Queries M EZPalTab Rev? • PAL constraints Classes 8 Slots . .forms i Instances M Queries Knowledge Acqiasition Classes & Instances Ouerv Is v + - siot JyJKzF iYTTT5" tcMEMB6l«HIP-«l*rL. ff|]R.rneml»r.of comams j r j j>Kostiandegan-tAMolAzlu J1 | ; Search Results (1) [ V I _ I Koshandegan-fAlKlol Azim Refuge) I , : i i M l l I • 1 Koshandegan (Abdol Az'rm Refuge) (type-RC-MEMBERSHIP RtL. . . • i_\ ™ " j c j x | _!?_L 1 1 C l e a r Query Name j Ft-has-menilier C -i-i Oehbahani W Hajl Sheikh Morteza I MirzaMostafa \% SadrOOtama ft Sheikh Mohamad Reza Uhomi i i description V^ho were the members of group Tosbandegan-CAbdol Azim refuge)'' 1 Query Library • Who was "Mirza Hossein Khan" T P Where/When was "Mare Hossein Khan" born? B Where/When was "Mirza Hossein Khan" died? 0 What true of honor did he hold and for how long? •. What positions did "Mirza Hossein Khan" hold (am) for how long)? What documents he made? © kt what events was he Involved 'Q Who were the members of group -Koshandegan 1 Abrlol Azim r elm f® Who was the super lot of "Mirza Hossein Khan" for each position tl I' SheHdl Mohamd Sadegh Kashani X Sled JamafeiSn Afteie W tahatahaie f -member -of V C + -t Kosliandegan (Abdol Azim Refuge) Rhas lima range j V C + . - A-group-type i OniologyVersion6_0t501 Religious Figure 4-46 Results for Competency Question #10 Question 10: Who were the members of group "Koshandegan-(Abdol-Azim refuge)"? This figure illustrates the results (right pane) obtained from the query stated above. By selecting a of the results, a pop up window (right side of figure) shows the members of the group, the group's name, and the time interval during which this group exists. Following a similar approach, each of the competency questions our model was designed to answer, were queried and tested. Chapter 5. Conclusions and Future Work 139 5 Conclusions and Future Work 5.1 Summary of thesis and results In this work we confronted the limitations of traditional electronic documents. In particular we were interested in capturing the semantic of a historical document in a manner that allows the user functionality beyond keyword search and allows reuse and sharing of the captured information. We selected to use an ontological approach to represent the information found in the book: the history of Iranian Constitution. Ontologies are often used to represent the semantic of the information in a domain by providing a consensual agreement amongst members of a community of interest. Ontologies not only allow representing hierarchical structures but can also be used to capture the relationships amongst concepts within a domain. This facilitates representing dynamic hierarchical structures such as governmental positions and their relations as well as geopolitical place hierarchies commonly found in a history domain. Another motivation for using ontologies is that they allow easy reuse and sharing of the knowledge. After a review of available ontology development environments, we selected Protege-2000 to formalize and instantiate our ontology. Our selection was based on the tool's expressiveness, flexibility, customizability, scalability, extensibility, and usability. Additionally, this tool provides us with a series of facilities to test and evaluate our model. Protege supports simple and complex queries and includes a couple of different graphical visualization plug-ins that allow visualizing and analyzing hierarchical structures contained within the ontology. The ontology was later evaluated by utilizing a set of competency questions and motivating scenarios we had defined previous to our implementation. The competency questions are the questions that the ontology must provide answer for and the motivating scenarios are the situations that the ontology should provide support for. The created model was successful in answering the questions as well as providing support for the chosen scenarios. Chapter 5. Conclusions and Future Work 140 5.2 Conclusions Our main purpose with this work was to examine the possibility of representing the knowledge found in a historical document in a manner that allows further computational manipulation than that what is provided by text or H T M L documents. In order to do this, we require a model where the representation of people, places, events and their relations are captured and understood at a computational level. This representation allows users to pose questions to the system that go beyond what is attainable by the currently available keyword searches. It was of utmost importance to us to allow this information to be reused and shared amongst users as well. Using an ontology, we extracted and represented the knowledge from the book "The History of the Iranian Constitution." Our implementation allowed us to get an overview of the general concepts in this book, relationships amongst these concepts and provided us with different methods for visualizing dynamic hierarchical structures of both governmental positions and geopolitical interdependencies. The user can get an insight into what happens in any place, in relation to any person in the book at any time. Additionally, this model captures the changes that these relations undergo through out time (dynamicity). The temporal aspect of the knowledge we captured proved to be useful in making our representation more accurate and realistic. 5.3 Future Work Due to time limitations and the scope of the proposed project, we were unable to develop every desirable extension to this work. In this section we present a couple of ideas for possible future work in this area. In order to facilitate the utilization of models such as the one developed here, we require to have applications that facilitate interacting with this information. As examples of such applications we might mention: • We would like to develop easy, intuitive interfaces to both access and query the information in the model. Developing such interfaces in a manner that allows people with different interests and backgrounds to access and use this information is a challenge left for future work. Chapter 5. Conclusions and Future Work 141 • Implementing a web-based representation of our ontology using schemas such as RDF or OWL. This facilitates reuse and sharing of this knowledge, and allows a greater audience for our information. Given our time constraints, we were unable to explore every possible research area related to our work. Additional areas of research we would like to explore include: • We based our design and ideas on information available in research papers and other articles referring to the history domain. In future work, we would additionally like to consult with historians and other domain experts to consider the usability issues and to develop a set of standards for our taxonomy. • In further work, we would like to design a guideline that establishes a clear path to follow for people interested in extracting and representing this kind of knowledge from historical text documents. As an example of this, we would like to explore the possibility of a joint research project with museum historians to facilitate capturing and representing the knowledge found in historical documents and artifacts. • Another area we would like to explore is designing and utilizing applications that automatically extract an ontological representation from text documents. 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An Ontological approach to representing historical knowledge
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