Web Service Description Requirements

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Abstract

This document describes the Web Service Description Working Group's requirements for the Web Service Description specification.

Status of this Document

This document is an editors' copy that has no official standing.

This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.

This is the first W3C Working Draft of the Web Service Description requirements document. It is a chartered deliverable of the Web Service Description Working Group (WG), which is part of the Web Service Activity. The Working has agreed to publish this document, although this document does not necessarily represent consensus within the Working Group about Web Service Description requirements.

Comments on this document should be sent to ws-desc-comments@w3.org (public archive[1]). It is inappropriate to send discussion emails to this address.

Discussion of this document takes place on the public ws-desc@w3.org mailing list[2] per the email communication rules in the Web Service Description Working Group Charter[3].

This is a public W3C Working Draft. It is a draft document and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite them as other than "work in progress". A list of all W3C technical reports can be found at http://www.w3.org/TR/.

Table of Contents

1 Notations
2 Relationship to WG Charter
3 Requirements on Requirements
4 Requirements
4.1 General Requirements
4.2 Simplicity
4.3 Interface Description
4.4 Description of Interactions with a Service
4.5 Binding Description
4.6 Mapping to the Semantic Web
5 Requirements from other W3C WGs
5.1 XML Protocol Requirements
5.2 XForms Requirements
5.3 RDF Requirements
6 References


1 Notations

The following terminology and typographical conventions have been used in this document.

Each requirement and scenario has a three digit number with a prefix indicating the status as follows:

  1. A "DRnnn" notation indicates a requirement that the WG is actively considering (has not reached rough consensus within the WG).

  2. An "Rnnn" notation indicates a requirement that the WG is not actively considering at present (has reached rough consensus within the WG).

The numbers used to identify requirements are arbitrary and does not imply any ordering or significance.

The document includes several verbatim quotes from the Web Service Description WG Charter[3] which provide context for the requirements. The quoted text is emphasized and prefixed with "Charter".

2 Relationship to WG Charter

The Web Service Description WG Charter[3] has two sections describing what is in-scope and what is out-of-scope of the problem space defined for the WG. The WG considers all the requirements in section 4 to be in-scope per the Charter.

Reviewers and readers should be familiar with the Web Service Description WG Charter[3] because it provides the critical context for the requirements and any discussion of them.

3 Requirements on Requirements

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4 Requirements

4.1 General Requirements

Charter: The language developed by the Working Group must not preclude any programming model, nor assume any particular mode of communication between peers.

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4.2 Simplicity

Charter: Focus must be put on simplicity, modularity and decentralization.

Charter: The language proposed must support the kind of extensibility actually seen on the Web: disparity of document formats and protocols used to communicate, mixing of XML vocabularies using XML namespaces, development of solutions in a distributed environment without a central authority, etc. In particular, it must support distributed extensibility.

Charter: Simplicity is a key element in making distributed systems easy to understand, implement, maintain, and evolve. Although simplicity can only be measured in relative terms, the Working Group must ensure that the complexity of any solution produced is comparable to that of other current and widespread Web solutions.

Charter: Another important aspect of simplicity is ease of deployment. The Working Group will look at various ways of deploying the Web services descriptions in a manner that is compatible with the existing Web infrastructure.

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4.3 Interface Description

Charter: The Working Group will define a description language expressed in XML. The description language must describe the messages available via the interface, accepted and generated by the Web service.

Charter: The language must also describe the error messages generated, if any.

Charter: The data exchanged is usually typed and structured. This increases interoperability by having applications agreeing on semantics and also provides some level of error detection. It is expected that developers will want to use different mechanisms for describing data types and structures, depending on the purpose of the Web service. The Working Group should allow different mechanisms, and must define one based on XML Schema.

Charter: The Working Group will also take into account the encoding work going on in the XML Protocol Working Group.

Charter: The Working Group will make sure that SOAP Version 1.2's extensibility mechanism can be expressed.

Charter: The description language designed will be used both by applications in order to automatically communicate between each other as well as by programmers developing Web services themselves. The language should therefore provide, in addition to the raw XML definition of the interface, human-readable comment capabilities to allow both applications and developers to make use of them.

Charter: Developers are likely to want to extend the functionality of an existing Web service. The Working Group will look into extending interface descriptions in a decentralized fashion, i.e. without priori agreement with the original interface designers.

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4.4 Description of Interactions with a Service

Charter: The Working Group will define a mechanism which will allow a Web service to describe the following set of operations: one-way messages (to and from the service described), request-response and solicit-response, as described in WSDL 1.1's port types.

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4.5 Binding Description

Charter: The information exchanged to and from a Web service can be carried in a large number of different ways. The action of carrying some XML-based communication in an underlying protocol is called, in the XML Protocol jargon, a binding. The description language defined should therefore describe how to reach the Web Service in a form which is orthogonal to its message exchange patterns and its messages.

Charter: It is expected that in the near-term future, Web services will be accessed largely through SOAP Version 1.2 (the XML- based protocol produced by the XML Protocol Working Group) carried over HTTP/1.1, or by means of simple HTTP/1.1 GET and POST requests. The Working Group will describe the following bindings:

  1. SOAP Version 1.2; SOAP can be used over a variety of underlying protocols; the Working Group will provide a concrete SOAP Version 1.2 over HTTP binding.

  2. HTTP/1.1 GET and POST requests.

Charter: The Working Group will also ensure that other SOAP bindings can be described.

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4.6 Mapping to the Semantic Web

Charter: The Working Group will provide a mapping to RDF so that the information described can be easily merged with that of other applications. This mapping will be developed with the help of the RDF Interest Group.

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5 Requirements from other W3C WGs

These are requirements submitted by other W3C Working Groups and Activities.

Note:

These are the verbatim received texts. The WG has not made any decisions regarding these requirements.

5.1 XML Protocol Requirements

5.2 XForms Requirements

5.3 RDF Requirements

6 References

1
Web Service Description Comments Archive (See http://lists.w3.org/Archives/Public/www-ws-desc-comments/.)
2
Web Service Discussion Archive (See http://lists.w3.org/Archives/Public/www-ws-desc/.)
3
Web Service Description Charter (See http://www.w3.org/2002/01/ws-desc-charter.)