Essential Business Process Modeling

Summary

The major points of this chapter are:

• Choreography is the attempt to build stateful, conversational, long-running, multiparticipant processes out of basic stateless, atomic web services operations.

• Orchestration is the coordination of web services within a single process. Choreography is coordination at the global level. Orchestration is subjective; choreography is subjective.

• The standards body behind the choreography effort is the W3C’s Choreography Working Group. The W3C’s other work on web services includes WSDL and SOAP, as well as the WS-* stack. WS-Choreography is one of its more recent contributions, and WS-CDL is its current— albeit unfinished—standard. Previous approaches, published on the W3C site but of diminishing importance, are WSCI and WSCL.

• WS-CDL is the officially endorsed W3C choreography language. A taut declarative language based on XML, WS-CDL presents a global view of a multiparty process and is especially suitable for B2B collaborations. The main concepts of WS-CDL are choreography, interaction, and channel. WS-CDL allows participants to pass around channels (web service-based communication links) in the spirit of the pi-calculus. A powerful feature of WS-CDL is that of guarded interactions, which initiate only if preconditions are met and can be configured to wait for all required data to become available before evaluating the precondition.

• WS-CDL is in its infancy. The specification is incomplete and is devoid of examples. WS-CDL’s future is hard to ...