What Is It?

WSDL, or Web Services Description Language, is an XML language used to describe network services as a set of endpoints that operate on messages that contain either document- or procedure-oriented information. The operations and messages are described abstractly and then bound to a concrete network protocol and message format to define an endpoint. Related concrete endpoints are combined into abstract endpoints or services. WSDL is extensible to allow description of endpoints and their messages regardless of what message formats or network protocols are used to communicate; however, the only bindings described in the W3C document describes how to use WSDL in conjunction with SOAP 1.1, HTTP GET/POST, and MIME.

WSDL 1.1 was submitted as a W3C Note by Ariba, IBM and Microsoft for describing services for the W3C XML Activity on XML Protocols in March 2001. The first Working Draft of WSDL 1.2 was released by W3C in July 2002.

Features

WSDK is written in XML, it is an XML document and that document is used to describe and locate Web services. It is not yet a W3C standard, but it is in draft mode. WSDL often is used in conjunction with SOAP and XML Schema to provide Web services over the Internet. A client program that cannects to a Web service can read the WSDL to determine which functions are available on the server.

Any special datatypes used by the server are embedded in the WSDL file in the XML Schema format. The client then uses SOAP to call a function listed in the WSDL.
In WSDL the term ‘binding’ refers to the process associating protocol or data format information with an abstract entity like a message, operation, or portType. WSDL allows extensibility elements or points of extensibility that typically are used to specify binding information for a particular protocol or message format, but that are not limited to those formats. Extensibility elements commonly are used to specify some technology-specific binding and must use an XML Namespace different from that of WSDL. Extensibility elements allow innovation in the area of network and message protocols without having to revise the base WSDL specification. WSDL recommends that specifications defining such protocols also define any necessary WSDL extensions used to describe those protocols or formats.

Who Is it For?

WSDL is provided for programmers and Web developers who already are familiar with XML, XML Namespaces and XML Schema. The logical frame of reference with WSDL usage also is a familiarity with SOAP.

Compatibility

WSDL is available to use across any server type that allows the use of XML and SOAP.

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