Requirements Modelling and Specification for Service Oriented Architecture

4.4. BPMN

Our second network notation for BPM is BPMN: Business Process Modelling Notation. Similar in general nature to activity diagrams, it is far more expressive and supports a mapping to the most popular process execution language: WS-BPEL. The downside of this is that it is ferociously complex - it has to be to support all the constructs of the BPEL programming language - but can be reasonably tamed for high level business process modelling. WS-BPEL is described briefly in Section 4.5.

The main constructs of BPMN are events, activities, flows and gateways. Flows, as one might expect, are shown as arrows which admit two decorations as shown in Figure 4-2. Undecorated arrows represent normal, unguarded flows between activities, events and gateways.

Default flows are used when flow splits into multiple paths dependent on the evaluation of some condition. Guarded flows are used when the flow is blocked unless the associated condition (guard) evaluates to TRUE. At once we can see that BPMN is slightly more complex than the activity diagram.

Figure 4.2. Special flows.

Figure 4.3. BPMN event types.

To give a further feel for the complexity and expressiveness of the notation, Figure 4-3 enumerates all the event types available in the specification. Event types are classified as ...