WSDL
Web Services Description Language (WSDL) is an eXtensible Markup Language (XML)-based description language that has been submitted to the World Wide Web Consortium (W3C) as the industry standard for describing Web services. The power of WSDL is derived from two main architectural principles: the ability to describe a set of business operations and the ability to separate the description into two basic units, a description of the operations and the details of how the operation and the information associated with it are packaged.
The WSDL document is the engine of a J2EE Web service; without it there is no service. The information within a WSDL file maps to the Java application to create a Web service. WebSphere Application Server Versions 5.0.2, 5.1 and 5.1.1 use standards based on WSDL 1.1.
A WSDL document allows a service provider to specify the name and address of the Web service; protocol and encoding style used when accessing the public operations of the Web service; and the type information, including name, operations, parameters and data comprising the interface of the Web service.
A WSDL document defines services as collections of network endpoints, or ports. In WSDL, the abstract definition of endpoints and messages is separated from their concrete network deployment or data format bindings. This allows the reuse of abstract definitions: messages, which are abstract descriptions of the data being exchanged, and port types which are abstract collections of operations. The concrete protocol and data format specifications for a particular port type constitutes a reusable binding. A port is defined by associating a network address with a reusable binding, and a collection of ports define a service. Therefore, a WSDL document is composed of several elements. See WSDL architecture for more information and examples of the WSDL elements.
When creating a Web service for WebSphere Application Server, first have an implementation bean that includes a Service Endpoint Interface. Then, you use the Java2WSDL command-line tool to create a WSDL that defines the Web service. To learn more about how the WSDL file is used in the development process, see Developing Web services.
Developing Web services based on Web Services for J2EE
Web services: Resources for learning
WSDL architecture
Java2WSDL command