BPM Milan: Instantiation Semantics for Process Models

Jan Mendling of Queensland University of Technology presented a paper on Instantiation Semantics for Process Models, co-authored with Gero Decker of HPI Potsdam. Their main focus was on determining the soundness of process models, particularly based on the entry points to processes.

They considered six different process notations and syntax: open workflow nets, YAWL, event-driven process chains, BPEL (the code, not a graphical representation), UML activity diagrams, and BPMN. They determined how an entry point is represented in each of these notations, with three different types of entry points: a start place (such as in open workflow nets), a start event (such as in BPMN), and a start condition (such as in event-driven process chains). He walked through a generic process execution environment, showing the entry points to process execution.

They created a framework called CASU: Creation (what triggers a new process instance), Activation (which of the multiple entry points are activated on creation), Subscription (which other start events are waited for upon the triggering of one start event), and Unsubscription (how long are the other start events waited for). Each of these four activities has several possible patterns, e.g., Creation can be based on a single condition, multiple events, or other patterns of events.

The CASU framework allows for the classification of the instantiation semantics of different modeling languages; he showed a classification table that evaluated each of the six process notations against the 5 Creation patterns, 5 Activation patterns, 3 Subscription patterns and 5 Unsubscription patterns, showing how well each notation supports each pattern. One important note is that BPEL and BPMN do not support the same patterns, meaning that there is not a 100% mapping between BPMN and BPEL: we all knew that, but it’s nice to see more research backing it up. 🙂

Having multiple start events in a process causes all sorts of problems in terms of understandability and soundness, and he doesn’t recommend this in general; however, since the notations support it and therefore it can be done in practice, analysis of multi-start point instantiation semantics is important to understand how the different modeling languages handle these situations.

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