A Note on Process Modelling: Combining Situation Calculus and Petri Nets
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The situation calculus logic model is convenient for modelling the actions that can occur in an information system application. The interplay of pre-conditions and post-conditions determines a semantically justified partial order of the defined actions and serves to enforce integrity constraints. This form of specification allows the use of plan-generation algorithms to investigate, before the system is adopted, whether the proposed specification allows all desirable use cases, and effectively disallows undesirable ones. Especially for legacy applications, implemented without a prior specification, Process Mining techniques were employed to derive an implicit Petri net model from the analysis of a large number of traces registered in an execution log. However, if the system just begins to be used, and has a still empty execution log, this sort of process mining discovery would not be feasible. This paper explains how the Petri net model can be directly derived from the situation calculus specification rules. The main gist is to provide evidence that the two models are complementary, not only because the Petri net model is derivable from the situation calculus model, but also in view of the distinct advantages of the two models. While the situation calculus model leads to planning and simulated execution prior to implementation, the Petri net model can be designed to run in a restrictive mode, allowing an intuitive visualization of the workable sequences. As proof of concept, the paper describes a prototype to demonstrate the methods and applies it to two examples: a published request processing application used to introduce process mining notions; and an analogously structured trial by combat application taken from a popular movie. The prototype includes an interactive dramatization component, which enacts the second application.
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