W3C | Submissions

Team Comment on Web Services Metadata Exchange 1.1 (WS-MetadataExchange)

W3C acknowledges receipt of the Web Services Metadata Exchange 1.1 (WS-MetadataExchange) Submission from Computer Associates, IBM, Microsoft, SAP AG, Sun Microsystems Inc. and Software AG.

WS-MetadataExchange defines how metadata relative to a specific Web Services endpoint might be addressed and retrieved, using WS-Transfer.

A Web Service may be defined by a set of metadata documents in order to allow other services or clients to interact with it. WSDL (describing the concrete binding used to communicate with it, the overall messaging operation as well as the message and data structures), WS-Policy (describing the requirements that a client should meet while talking to this service) and XML Schema (used in WSDL, or externally to describe the structure and data types of the messages) are the metadata documents addressed by this Submission, although the mechanism is open to other kind of metadata.

In this document, the version of WSDL used is WSDL 1.1 (W3C Member Submission) and the version of WS-Policy is also the W3C Member Submission. More recent W3C Recommendations are available, see WSDL 2.0 and WS-Policy 1.5.

This Submission defines an encapsulation mechanism, used to transport and identify the metadata and its type (Policy, WSDL, Schema). In the definition of a Metadata Section, several properties are used:

Identifying the type of Metadata
The Endpoint Reference (EPR) of the metadata resource
The URL of the metadata resource

The Dialect property might be seen as being in conflict with the use of Media Types used to identify the different formats, however the fact that XML Schema does not have a specific Media Type (it uses application/xml) makes this addition a solution to the negotiation of the metadata.

Also there are different way to access those metadata, via an Endpoint Reference, or an URL. In the case of an URL, it is not clear that there will be a direct retreival using the native protocol of the URL, or a SOAP interaction using WS-Transfer at that particular URI. In the latter case comments made about WS-Transfer apply.

It is also possible to embed metadata fragments in an EPR, but in this case the issue of the authoritative version of those metadata is open.

Next steps

The W3C Team plans to notify the Web Services Coordination Group of this Member Submission. As there are existing plans to start new work on the subject covered by this Submission, it could be used as an input document by the Working Group.

Authors: Yves Lafon
$Date: 2008/09/01 13:10:14 $