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UBC Theses and Dissertations

Reasoning tools to support systems analysis and design Paulson, James Daniel


Some parts of the systems analysis and design process are not well structured and rely heavily on human judgement and experience. This is particularly true for decomposition and the validation of system specifications. Decomposition has long been considered a fundamental part of systems analysis and design. However, ensuring that a decomposition is optimal is nearly impossible. Ensuring that a system specification is complete and consistent is an inherently difficult task. Most existing systems analysis and design methodologies allow only the use of techniques such as code walk-throughs and post-implementation testing. Analysis errors discovered at such late stages can be quite expensive to correct. Existing methodologies cannot support automated completeness and consistency testing because they lack the degree of formalism required to allow automation. The primary objective of this research was to increase understanding of system decomposition. To aid in achieving this objective a formalism for representing a system specification, and a set of computer-based specifications analysis tools were developed. The tools support decomposition and provide completeness and consistency testing of a system specification. An existing system modelling formalism was extended to provide the basis for the specification formalism. This extended formalism will allow an analyst to describe a system with the degree of precision necessary for automated testing and decomposition. The ability to create a complete and consistent system model facilitated the development of a general theory of system decomposition. A system model created using the specifications analysis tools can be analyzed using a decomposition algorithm based on this theory. The algorithm incorporates a number of commonsense software design rules and decomposition heuristics drawn from the literature, and has been included in the specifications analysis tools. Experience has shown that the specifications analysis tools may suggest system decompositions not previously considered by the analyst. Alternative decompositions may arise in two situations: 1. The system has a valid alternative structure which may not have been considered by the analyst. This alternative structure may be superior to the original structure envisioned by the analyst when the system model was constructed. 2. The system specification does not contain enough information to rule out certain unreasonable decompositions. The missing information should be explicitly included in the specification to avoid problems of interpretation later in the system development life cycle. Analysis of several test systems (including the IFIP Working Conference system often used as a standard problem in the systems analysis literature) using the specifications analysis tools has proven the feasibility of automated consistency and completeness testing and decomposition. Further research is required in two areas: 1. Enhancement of the specifications analysis tools. The tools are not user friendly. An analyst will require extensive training to use them effectively. As well, the computational speed of the tools must be improved. Automated decomposition is too slow to allow easy interaction between the analyst and the tools. 2. A hierarchical analysis technique must be developed to support application of the specification formalism and the theory of decomposition to larger systems.

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