WSDL 2.0, new messaging for Web services

The Web Services Description Language, or WSDL, has been in circulation since 2001, when the first version was circulated from the W3C while still under development. This was followed by a working draft of version 1.2 in July 2002 that stood until June of 2007, at which point the W3C released new recommendations for WSDL 2.0:

• Web Services Description Language (WSDL) Version 2.0 Part 0: Primer
• Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language and Schema
• Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts
• SOAP 1.2 binding schema, HTTP binding schema, RPC extension schema, wsdlx schema

There's a lot of helpful new functionality in WSDL 2.0 and some equally helpful reductions in capability, including:

• New semantics for the description language, including making targetNamespace a required attribute for the definitions element
• Delegation of message constructs and handling to XML schema types referenced in the types element
• Operator overloading remains absent (it was removed in the transition from WSDL 1.1 to 1.2, and stays out in 2.0)
• The ports element is renamed as endpoints and PortTypes becomes interfaces, where interface inheritance is supported by the extends attribute in the interface element.

At the most fundamental level, Web services in WSDL 2.0 are modeled using abstract and concrete parts. On the abstract side, a Web service is described according to the messages it emits and receives through a type system, typically XML Schema (though RELAX NG also works). Message exchange patterns describe their allowed sequences and ordering, where operation elements associate message exchange patterns with at least one message, and an interface element groups operations to be independent of transport and network access techniques. On the concrete side, bindings step in to define transport and network access formats and service endpoint elements associate network addresses with bindings. Service elements group endpoints to implement a shared interface.

For more details on this new specification, plus lots of markup examples and illustrations, see Arulazi Dhesiaseelan's excellent article for XML.com "What's New in WDSL 2.0."

About the author

Ed Tittel is a full-time writer and trainer whose interests include XML and development topics, along with IT Certification and information security topics. Among his many XML projects are XML For Dummies, 4th edition, (Wylie, 2005) and the Shaum's Easy Outline of XML (McGraw-Hill, 2004). E-mail Ed at etittel@techtarget.com with comments, questions or suggested topics or tools for review.