Walking Through the Semantics of Exclusive and Event-Based Gateways in BPMN Choreographies

With the evolution of distributed systems, nowadays BPMN choreography diagrams have acquired more and more importance for modelling systems interaction. However, one of the drawbacks of this model is the lack of formal semantics, which leads to different interpretations, and hence implementations, of some of its features. Among the BPMN choreography elements, particularly ambiguous is the semantics of the exclusive and event-based gateways, used to represent different forms of choices. Formalisations of these elements have been proposed in the literature, but none of them is derived from a direct and faithful modelling of the description provided by the BPMN standard. In this work, instead, we provide a direct formalisation, in terms of an operational semantics, that aims at shedding light on the intricacies of the behaviour of the exclusive and event-based gateways. The effectiveness of the approach is shown by illustrating how our semantics can disambiguate tricky behaviours in choreography models.