Web Services Business Process Execution Language Version 0 Public Review Draft 02, 20 November, 2006

XSD Schemas are provided as a definition of grammars [XML Schema Part 1]. Where there is disagreement between the separate XML schema files, the XML schemas in the appendices, any pseudo-schema in the descriptive text, and the normative descriptive text, the normative descriptive text will take precedence over the separate XML Schema files. The separate XML Schema files take precedence over any pseudo-schema and over any XML schema included in the appendices. The WS-BPEL XML Schemas offer supplementary normative XML syntax details, such as details regarding extensibility of a WS-BPEL process definition, as long as those XML syntax details do not violate explicit normative descriptive text.

XML Schemas only enforce a subset of constraints described in the normative descriptive text. Hence, a WS-BPEL artifact, such as a process definition, can be valid according to the XML Schemas only but not valid according to the normative descriptive text.

This specification uses a number of namespace prefixes throughout; their associated URIs are listed below. Note that the choice of any namespace prefix is arbitrary, non-normative and not semantically significant.

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  xsi - "http://www.w3.org/2001/XMLSchema-instance"
  
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  xsd - "http://www.w3.org/2001/XMLSchema"
  
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  wsdl - "http://schemas.xmlsoap.org/wsdl/"
  
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  vprop - "http://docs.oasis-open.org/wsbpel/2.0/varprop"
  
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  sref - "http://docs.oasis-open.org/wsbpel/2.0/serviceref"
  
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  plnk – "http://docs.oasis-open.org/wsbpel/2.0/plnktype"
  
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  bpel – "http://docs.oasis-open.org/wsbpel/2.0/process/executable"
  
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  abstract – "http://docs.oasis-open.org/wsbpel/2.0/process/abstract"
  

3. Relationship with Other Specifications

WSDL has the most influence on the WS-BPEL language. The WS-BPEL process model is layered on top of the service model defined by WSDL 1.1. At the core of the WS-BPEL process model is the notion of peer-to-peer interaction between services described in WSDL; both the process and its partners are exposed as WSDL services. A business process defines how to coordinate the interactions between a process instance and its partners. In this sense, a WS-BPEL process definition provides and/or uses one or more WSDL services, and provides the description of the behavior and interactions of a process instance relative to its partners and resources through Web Service interfaces. That is, WS-BPEL is used to describe the message exchanges followed by the business process of a specific role in the interaction.

The definition of a WS-BPEL business process follows the WSDL model of separation between the abstract message contents used by the business process and deployment information (messages and port type versus binding and address information). In particular, a WS-BPEL process represents all partners and interactions with these partners in terms of abstract WSDL interfaces (port types and operations); no references are made to the actual services used by a process instance. WS-BPEL does not make any assumptions about the WSDL binding. Constraints, ambiguities, provided or missing capabilities of WSDL bindings are out of scope of this specification.

However, the abstract part of WSDL does not define the constraints imposed on the communication patterns supported by the concrete bindings. Therefore a WS-BPEL process may define behavior relative to a partner service that is not supported by all possible bindings, and it may happen that some bindings are invalid for a WS-BPEL process definition.

While WS-BPEL attempts to provide as much compatibility with WSDL 1.1 as possible there are three areas where such compatibility is not feasible.

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  Fault naming with its restriction, as discussed later in this document (see section 10.3. Invoking Web Service Operations – Invoke)
  
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  [SA00002] Overloaded operation names in WSDL port types. Regardless of whether the WS-I Basic Profile configuration is enabled, a WS-BPEL processor MUST reject any WSDL port type definition that includes overloaded operation names. This restriction was deemed appropriate as overloaded operations are rare, they are actually banned in the WS-I Basic Profile and supporting them was felt to introduce more complexity than benefit.
  
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  [SA00001] Port types that contain solicit-response or notification operations as defined in the WSDL 1.1 specification. Regardless of whether the WS-I Basic Profile configuration is enabled, a WS-BPEL processor MUST reject a WS-BPEL that refers to such port types.
  

It should be noted that the examples provided in this specification adopt the Schema at location "http://schemas.xmlsoap.org/wsdl/2004-08-24.xsd" for the namespace URI http://schemas.xmlsoap.org/wsdl/ [WSDL 1.1]. This XML Schema incorporates fixes for known errors, and is the XML Schema selected by the [WS-I Basic Profile 1.1 Errata] (October 25, 2005).