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Team Comment on the "Web Services Description Language (WSDL) 1.1" Submission

W3C is pleased to receive the Web Services Description Language (WSDL) 1.1 submission from International Business Machines Corporation, Microsoft Corporation, Allaire, Ariba, BEA, Bowstreet, Commerce One, Compaq Computer Corporation, DataChannel, Epicentric, Fujitsu Limited, Hewlett-Packard, Intel, IONA Technologies, Jamcracker, Lotus Development Corporation, Oracle, Rogue Wave, SAP, TIBCO, VeriSign, Vitria, webMethods, XML Global Technologies and XMLSolutions.

Today's Web offers many information- and computing services such as stock quote services, calculators for mortgage payments, or databases for learning details about particular movies. Many of these services are geared towards a human user, i.e. a human fills in input parameters in a Web form, and the results are delivered as part of an HTML file. It is often very useful to reuse these services as part of a computer program that does further processing of the results delivered by the service. However, this is difficult today due to the orientation of the existing services towards a human user. For example, it requires using awkward "screen scraping" approaches in order to extract the results of a query from HTML source code.

The WSDL submission allows building web-based information- and computing-services targeted to computer programs rather than to human users. It allows using an XML-based language to describe Web Services in terms of the type and number of parameters passed to a service, the type and structure of the result returned etc. WSDL also gives example mappings of WSDL descriptions onto a number of Web protocols that can be used for passing parameters and results (SOAP, URL-encoded parameter passing in HTTP and multipart MIME transported via HTTP).

WSDL relates to the following W3C Activities and Groups:

XML Schema
WSDL uses XML Schema as its default mechanism for defining the structure of messages exchanged by a particular service, and the data type of the parameters and results passed in these messages.
XML Protocol
The submitters propose that WSDL should be taken up by a newly created Working Group in the XML Protocol Activity. The services defined in a WSDL description could be mapped onto the protocol to be developed by the XML Protocol WG.
XForms is a technology that is being designed to replace HTML Forms, which is the method human users are employing today to interact with Web Services. The current design of XForms shows a number of interesting parallels with the WSDL submission. For one, both technologies allow use of alternative protocols for parameter-passing (XML-encoding, URL-encoded parameters, multipart MIME). Moreover, both WSDL and XForms also separate the definition of the data structures exchanged by the Web Service from their bindings to particular operations. Finally, XForms includes a constraint mechanism for validating user input to a form. A similar mechanism could be used in a WSDL-like technology to express high-level consistency-constraints between the parameters in the messages exchanged. Overall, it would be interesting to explore opportunities for technology sharing and alignement between WSDL-like approaches and XForms.
Semantic Web
The Semantic Web activity page describes the vision for the Semantic Web as "the idea of having data on the Web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration and reuse of data across various applications". The WSDL submission appears to contribute to this vision by enabling use of Web services by computers. A November 2000 article, Web services : WSDL processing with XSLT by Uche Ogbuji, demonstrates integration of WSDL and RDF.
When evaluating the integration of the WSDL submission into the Web Architecture, the proposed facility for generating URIs that are not globally unique for all time may require further study. Specifically, it appears risky to assume that two people could choose to simultaneously use the same URI for two completely different Schemas under the assumption that the scope of the use of the URIs will not intersect. In a completely decentralized system such as the Web, collision at some point in the future can never be fully excluded.

Next Steps

To determine the next steps in the Web Services area, W3C will be holding a Workshop on Web Services. The submitters of WSDL are encouraged to submit a position paper to this Workshop. Moreover, the community is invited to provide feedback on this submission to www-ws@w3.org (see also how to subscribe to a W3C mailing list).

Disclaimer: Placing a Submission on a Working Group/Interest Group agenda does not imply endorsement by either the W3C Staff or the participants of the Working Group/Interest Group, nor does it guarantee that the Working Group/Interest Group will agree to take any specific action on a Submission.

Update (HH - 2003-06-18): In January 2002, W3C started the Web Services Description Working Group to address the area of Web service description. This Working Group uses the technical solution offered by WSDL 1.1 as the basis for its work. Please refer to the Working Group charter and the Web Services Activity statement for details.

Philipp Hoschka, Architecture Domain Leader <ph@w3.org>
$Date: 2003/06/18 12:51:02 $