BPEL and Its Relation to BPML, WSCI, WSFL, Xlang, and Others

In a domain with such a perceived widespread need as business process management for Web services, it is not surprising that several efforts outside of BPEL have proposed alternative solutions. Indeed, work is still ongoing with such efforts as it is with BPEL itself.

One alternative approach, BPML (Business Process Modeling Language), considers e-business processes as made of a common public interface and of many private implementations as process participants. This enables the public interface of BPML processes to be described as ebXML business processes or RosettaNet Partner Interface Processes, independently of their private implementations.

In much the same way XML documents are usually described in a specific XML Schema, BPML processes can be described in a specific business process modeling language layered on top of the BPML XML Schema. BPML represents business processes as the interleaving of control flow, data flow, and event flow, while adding orthogonal design capabilities for business rules, security roles, and transaction contexts.^[9]

^[9] From http://www.bpml.org.

Another alternative, WSCI (Web Services Choreography Interface), is somewhat of a half-way house between WSCL and BPEL since it concentrates on the details of the ins and outs of a specific endpoint and scales this out to multiparty choreography by the use of connectors that link the outputs from service invocations to the inputs of others. In common with BPEL, WSCI can handle message correlation, properties and so forth automatically. However, its strength in describing the behavior of individual endpoints is reflected in the fact that it supports such notions as transaction and compensation boundaries.

WSCL (see Chapter 5) is also sometimes thought of as a choreography language, though it is considered separately since it deals with choreographing individual service endpoints, which is an orthogonal issue (and complementary) to business process orchestration.

IBM's WSFL and Microsoft's Xlang have similar goals to BPEL and indeed it is the convergence of these two technologies that ultimately yielded the BPEL specification. Xlang in particular has a good heritage since it is widely deployed in B2B scenarios, being the lingua franca of Microsoft's BizTalk server B2B platform.

Although the world of business process choreography for Web services is still in a state of flux, BPEL is the clear leader, having come from the most eminent Web services vendors and due to the fact that it is a second generation technology while others remain in their first iteration. Though there may be convergence over time, the general principles, if not the majority of the syntax and language constructs, set out by BPEL are likely to be pervasive within this domain.