The W3C Web Services Description Working Group has posted three revised candidate recommendations and two working drafts for WSDL 2.0:
"Web Services Description Language Version 2.0 (WSDL 2.0) provides a model and an XML format for describing Web services. WSDL 2.0 enables one to separate the description of the abstract functionality offered by a service from concrete details of a service description such as 'how' and 'where' that functionality is offered. This specification defines a language for describing the abstract functionality of a service as well as a framework for describing the concrete details of a service description. "
WSDL is an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information. Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts defines predefined extensions for use in WSDL 2.0:
Message exchange patterns
Operation styles
Binding Extensions
"This document is a companion to the WSDL 2.0 specification (Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language [WSDL 2.0 Core], Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts [WSDL 2.0 Adjuncts]). It is intended for readers who wish to have an easier, less technical introduction to the main features of the language."
"WSDL SOAP 1.1 Binding (this specification) describes the binding extension for SOAP 1.1 [SOAP11] protocol. This binding is intended to ease the migration from WSDL 1.1 to WSDL 2.0 for implementers describing services that use SOAP 1.1 protocol. And, this binding allows users to continue using SOAP 1.1 protocol."
Web Services Description Language is defined in XML, because XML is the standard format for exchange of structured information. The use of XML brings better interoperability to WSDL generators and parsers, and the use of XML Schema makes the structure of WSDL well constrained, yet extensible. On the other hand, XML vocabularies in general don't have clear composition rules, so combining for example the WSDL description of a Web service, the service's policies and other information (presumably expressed in XML) can be done in many significantly different ways (e.g. extending WSDL, extending the policy language, creating a special XML container for all the information etc.), and little interoperability can be expected when such combined documents are used.
For example, a policy can be combined with WSDL by adding the policy elements in WSDL service element. Equally, a WSDL description can be combined with a policy by adding the WSDL description as part of the policy. While the results should be similar (WSDL with policy information), they are in fact very different for the processing software, and a policy in WSDL cannot easily be used by software that doesn't know WSDL.
In contrast, the Semantic web requires knowledge from many different sources to be easily combined so that unexpected data connections can be used. For this purpose there is the Resource Description Framework (RDF), whose graph structure together with the use of URIs for identifying nodes makes it very easy for different documents to be brought together. If a WSDL document describes a Web service, a policy document attaches constraints to the service and a general description specifies the author of the service, all this information can be merged and the resulting document will contain all the three kinds of information associated with the single service.
The main objective of this specification is to present a standard RDF ([RDF]) and OWL ([OWL]) vocabulary equivalent to WSDL 2, so that WSDL 2 documents can be transformed into RDF and merged with other Semantic Web data.
Comments are due by July 1.
