BPMN11 — Use of link events to synchronize behaviour

These issues refer to the examples in section 10.2.1 Normal Flow in the BPMN Adopted Specification as of february 2006; pages 125-128.

A problem with the use of Link events for synchronizing behaviour is that there also is a need to explicitly state that two link events are the same object. This can be indicated through the use of (directed or undirected) associations, but that still is an indication only; not formalized. Next, use of such "equality associations" has problems with cases where the "same event" occurs both as an end event and a start event, as seen in figure 10.49. Here, the two "B Completed" link events are probably not exactly the same object (with the same id) since they are of different (sub)types.
Such use of link events, which I do indeed consider very useful, should be improved in upcoming versions of BPMN.

Two possible solutions for this could be:

1) Introduce a way of specifying that two flow objects within/across diagrams are "equal"; possibly also allowing equality across start and end events. Could be a particular kind of associons with strong semantics.

2) The situation in figure 10.49 is quite similar to "message exchange" - but within a pool. Just as there has been identified a need for distinguishing between sending and receving intermediate message events, there is a similar need to distinguish between "generating" and "reacting" intermediate link events. Generating intermediate link events could have the existing symbol; one can pragmatically think of them as "Go-to's". Reacting intermediate link events could have a new symbol with the internal fat arrow pointing right to left; these can be thought of as "Comes-from's". In the example then the topmost "B Completed" event could be changed into an generating intermediate link event. The bottom fragment could be changed into a normal start event, followed by a reacting intermediate "B Completed" link event followed by task D. There also must be some way of "pairing" the related generating and reacting events; this could be done by adding an attribute to the receiving event which holds the id of the matching generating event.

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