Web Services Description Language (WSDL)

WSDL 1.0 was introduced in 2000 and was developed through a collaboration by Microsoft, IBM and Ariba. The language was formalized in 2001 as version 1.1.

WSDL 2.0 is substantially different from version 1.1 and was endorsed as a W3C recommendation in 2007. Most third-party vendors, however, have not adapted their offerings to support WSDL 2.0. For example, the Web Services Business Process Execution Language (WS-BPEL) uses WSDL 1.1.

A WSDL 2.0 service description indicates how potential clients should interact with the described service. A WSDL document describes two aspects of a Web service: one abstract and one concrete.

In the description that follows, WSDL elements are italicized.

1. At an abstract level, the Web service is described in terms of the messages it sends and receives. An operation associates a message exchange pattern with one or more messages. A message exchange pattern identifies the sequence and cardinality of messages sent and/or received as well as who they are logically sent to and/or received from. An interface groups operations together without committing to transport or wire format.
   
2. At a concrete level, a binding specifies transport and wire format details for one or more interfaces. An endpoint associates a network address with a binding. And finally, a service groups together endpoints that implement a common interface.