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Team Comment on the WS-Addressing Submission

W3C is pleased to receive the Web Services Addressing (WS-Addressing) submission from BEA Systems, IBM, Microsoft, SAP AG, and Sun Microsystems, Inc..

The WS-Addressing specification provides transport-neutral mechanisms to address messages and identify Web services, corresponding to the concepts of address and message correlation described in the Web Services Architecture.

WS-Addressing defines two constructs to that end:

• Endpoint references, which identify the message destination.
• Message information headers, which allow the specification of endpoint references within messages, along with a way to relate messages to each other.

Relationship to W3C work

This specification relates to work that is being done under the Web Services Activity:

• Web Services Description Language (WSDL) 2.0: the endpoint reference description and the [action] property defined by WS-Addressing are related to the description of a Web service that may be expressed in a WSDL 2.0 document.
• SOAP Version 1.2: WS-Addressing message information headers are an extension to the SOAP 1.2 messaging framework.

Relationship to the Web Services Description Language (WSDL)

In WS-Addressing, an endpoint reference is presented as a complement to the concept of a WSDL service. The [selected port type] and [selected port] properties correspond to those of the WSDL 1.1 Member Submission description of a service, and the [action] property is derived from this description.

However, WS-Addressing does not specify its relationship to WSDL 2.0. We note that the mechanisms used by WS-Addressing to reference WSDL components differ from the mechanisms introduced by WSDL 2.0 to reference WSDL constructs.

WS-Addressing may be used in a message exchange described by a WSDL document. It would be useful to document the relationship between the values of the message information headers and the WSDL components of the description, in particular when WS-Addressing is used in the context of the WSDL 2.0 predefined message exchange patterns.

Relationship to SOAP

A binding of message information headers to SOAP is provided, both to the SOAP 1.2 Recommendation and to the SOAP 1.1 submission.

However, the binding to SOAP 1.2 does not define WS-Addressing as a SOAP 1.2 module as it does not define a URI in order for WS-Addressing to be referenced in description languages (such as WSDL 2.0) or during negotiation. Also, WS-Addressing's [action] property can be directly mapped to SOAP 1.2's SOAP Action Feature's http://www.w3.org/2003/05/soap/features/action/Action property.

It is also worth noting that WS-Addressing does not define how the message information headers' abstract properties could be serialized out of the SOAP envelope when the SOAP message is bound to the HTTP underlying protocol. Considering the SOAP 1.2 HTTP binding which supports the SOAP Action Feature, the [action] property can be carried in the action parameter. For HTTP requests, the [destination] property may be carried by the HTTP/1.1 Request URI.

Relationship to other Member Submissions

It is interesting to compare this submission to the WS-MessageDelivery Submission. For example, WS-Addressing defines a [policy] endpoint reference property to carry policy statements, while WS-MessageDelivery does not. Also, while WS-MessageDelivery takes an approach which is derived from WSDL for referencing Web services, WS-Addressing is providing a SOAP extension using a more lightweight description.

Other considerations

• The WS-Addressing [policy] property specifically uses another proposal by BEA Systems Inc., International Business Machines Corporation, Microsoft Corporation, and SAP AG, WS-Policy, thus creating a dependency on WS-Policy. This mechanism is interesting to consider in the context of the upcoming W3C Workshop on Constraints and Capabilities for Web Services.
• The motivation and use cases for [reference properties] and [reference parameters] are unclear, since similar information could be provided in other ways, such as using the Application Data Feature defined in WSDL 2.0 Part 2, or another SOAP extension.

Next steps

This new submission on the topic of Web services references and message delivery highlights the community's interest in this area. The W3C is considering creating a Working Group to address this important area of the Web services architecture.

Feedback on this technology is encouraged on the www-ws@w3.org mailing list (public archive).