BPEL4WS (Business Process Execution Language for Web Services) enables the specification of executable business processes (including Web services) and business process protocols in terms of their execution logic or control flow. Executable business processes specify the behaviour of individual participants within Web service interactions and can be invoked directly, whereas business process protocols (also called abstract processes) abstract from internal behaviour to describe the messages exchanged by the various Web services within an interaction.

Abstract processes only consider protocol-relevant data and ignore process-internal data and computation. The effects of such computation on the business protocol are then described using non-deterministic data values. Executable processes, on the other hand, are described using a rich process description language which deals with both protocol-relevant and process-internal data. Executable processes also reference port types contained in WSDL documents, which are used to define partner roles that can be filled by those Web services that meet the restrictions set for the partner role. These roles can thus be filled dynamically and the port-specific information of the partner bound at run-time. BPEL4WS also defines several mechanisms for recovery from faults, such as catching and handling of faults, and compensation handlers which specify compensatory activities in the event of actions that cannot be explicitly undone.

While there is overlap in the conceptual models of OWL-S and BPEL4WS, OWL-S truly complements BPEL4WS. Recent work has shown how BPEL4WS can leverage rich OWL-S descriptions of services to augment its functionality to include tasks such as dynamic partner binding and semantic integration, e.g., [25]. OWL-S aims to make Web services computer-interpretable -- described with sufficient information to enable automation of a variety of tasks including Web service discovery, invocation, and composition. BPEL4WS has no such objective. It provides a language for describing executable processes and protocols that are constructed manually.

At its core, BPEL4WS is a process modeling language that draws heavily from previous Web services specifications, such as XLANG [22] and WSFL [23]. As such, it relates most closely with the OWL-S Process Model. OWL-S leverages the rich expressive power of OWL together with its well-defined semantics to provide richer descriptions of Web services that include process preconditions and effects. This enables the encoding of service side-effects that are often important for automated selection and composition of Web services. OWL-S also provides for the description of non-functional service constraints that are useful for automated Web service discovery or partnership bindings. Finally, OWL-S enables rich typing of Web service parameters including properties of objects and complex constraints between them. At present the OWL-S process model differs from BPEL4WS in that it masks some execution details of Web services. Nevertheless, the OWL-S process model was designed with the objective of encompassing emerging process model standards such as BPEL4WS. OWL-S currently does not define recovery protocols but the formalised translations of OWL-S descriptions (as in [10, 9]) may be extended to support them.

以下是引用zhengfrance在2007-4-5 16:34:00的发言： 看了些英文资料，还是弄不太懂