Advanced BPMN: Subprocesses, Boundary Events, Compensation, Choreography
Scope
Advanced constructs exam questions probe: subprocess flavours, boundary events, compensation semantics and choreography for cross-organisational views.
Core rules
- Embedded subprocess is defined in place; a call activity references a reusable global process, so one definition serves many parents.
- Event subprocess sits in a scope with no incoming or outgoing sequence flows; a solid start-event border interrupts the scope, a dashed border runs non-interrupting alongside it.
- Boundary event attaches to an activity or subprocess. Interrupting (solid) cancels the activity; non-interrupting (dashed) spawns a parallel branch while the activity continues. Only one interrupting boundary event can fire per activity instance.
- Compensation: a compensation boundary event attaches a handler that does not run as a normal outgoing flow; it runs only when a compensate throw event is reached or a transaction is cancelled. Handlers execute in reverse completion order.
- Choreography: choreography tasks between two participant bands, sub-choreographies, and message exchanges. It shows interactions, not either party's internal logic.
Worked example
Goods are prepared within a two-hour window. Attach a non-interrupting timer boundary event (2h) to 'Prepare shipment': on firing, 'Escalate to dispatcher' starts in parallel and preparation continues. Reasoning: choosing the interrupting variant instead would cancel preparation, so the marker, not the drawing, carries the semantics.
Traps that cost marks
Treating a compensation handler as an error handler, when it is thrown explicitly. Confusing an interrupting boundary event with an event subprocess in the same scope. Drawing a choreography as a collapsed pool plus message flows.