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UBC Theses and Dissertations

TSPN[sub UI]: a petri net model for specifying user interactions in multimedia presentations Cooper, Kendra M. L.


The first objective of this thesis is to analyze and group the synchronization requirements for a generic, distributed, multimedia presentation application [Gon95a]. The purpose of this analysis work is to determine what synchronization requirements a general purpose specification approach for distributed multimedia applications must be able to describe. The results reveal a set of related requirements, which are classified into four categories: data stream; communication; computer-human interaction; and expressiveness requirements. The analysis and classification work provides a template which may be tailored for specifying applications. The second objective of this thesis is to review Petri net models. Established Petri net models are reviewed in addition to recent multimedia extensions [Gon95b, Vuo95a]. The multimedia extensions are the Object Composition Petri net (OCPN), Extended Object Composition Petri Net (XOCPN), Dynamic Timed Petri net (DTPN), and the Time Stream Petri net (TSPN). The purpose of this analysis is to determine which requirements each of the Petri net approaches may model. The analysis work is carried out using an illustrative example, which includes interstream and intrastream synchronization, time dependent and time independent data streams, fixed playout duration, coarse and fine grained synchronization requirements, user interactions, and jitter constraints. The example is specified in the natural language and the multimedia Petri net extensions. The analysis of these specifications focuses on whether or not a model may be used to describe the requirements and how complex the resulting model is" in terms of the number of symbols used to describe the example. The results of this work indicate that the TSPN approach provides a good basis for describing multimedia applications, but needs to be enhanced to describe pre-emptive user interactions, quality of service, and multiple destination site requirements. The third objective of this thesis is to extend the TSPN model to permit the formal modelling of pre-emptive user interactions. The newly enhanced version is called the TSPNyII model. The TSPN model is used as the basis of the extension because it models a large number of the synchronization requirements for a generic multimedia application. The pre-emptive user interaction approach in the DTPN model is simplified, generalized into a toolkit of interactions, and integrated with the TSPN approach. To insure the temporal correctness of the TSPNII extension, the example is simulated using a visualization tool developed with MATLAB [MAT94]. MATLAB is a commercial application which has been successfully used to simulate Petri nets [Rez95]. The simulation tests different scenarios of user interactions and timing of events to verify the model maintains synchronization under diverse conditions. Errors in the specification are found and corrected using the Visualization Tool. The practical significance of the tool is that error detection and correction are less expensive early in the development cycle.

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