14 Mapping BPMN Models to WS-BPEL

14.1 General

NOTE: The contents of this clause is REQUIRED for BPMN BPEL Process Execution Conformance or for BPMN Complete Conformance. However, this clause is NOT REQUIRED for BPMN Process Modeling Conformance, BPMN Process Choreography Conformance, or BPMN Process Execution Conformance. For more information about BPMN conformance types, see page 1.

This clause covers a mapping of a BPMN model to WS-BPEL that is derived by analyzing the BPMN objects and the relationships between these objects.

A Business Process Diagram can be made up of a set of (semi-) independent components, which are shown as separate Pools, each of which represents an orchestration Process. There is not a specific mapping of the diagram itself, but rather, each of these orchestration Processes maps to an individual WS-BPEL process.

Not all BPMN orchestration Processes can be mapped to WS-BPEL in a straight-forward way. That is because BPMN allows the modeler to draw almost arbitrary graphs to model control flow, whereas in WS-BPEL, there are certain restrictions such as control-flow being either block-structured or not containing cycles. For example, an unstructured loop cannot directly be represented in WS-BPEL.

To map a BPMN orchestration Process to WS-BPEL it MUST be sound, that is it MUST contain neither a deadlock nor a lack of synchronization. A deadlock is a reachable state of the Process that contains a token on some Sequence Flow that cannot be removed in any possible future. A lack of synchronization is a reachable state of the Process where there is more than one token on some Sequence Flow. For further explanation of these terms, we refer to the literature. To define the structure of BPMN Processes, we introduce the following concepts and terminology. The Gateways and the Sequence Flows of the BPMN orchestration Process form a directed graph. A block of the diagram is a connected sub-graph that is connected to the rest of the graph only through exactly two Sequence Flows: exactly one Sequence Flow entering the block and exactly one Sequence Flow leaving the block. A block hierarchy for a Process model is a set of blocks of the Process model in which each pair of blocks is either nested or disjoint and which contains the maximal block (i.e., the whole Process model) A block that is nested in another block B is also called a subblock of B (cf. Figure 14.1). Each block of the block hierarchy of a given BPMN orchestration Process has a certain structure (or pattern) that provides the basis for defining the BPEL mapping.