Web Service Description Language

WSDL is an XML-based language for describing Web services and how to access them. WSDL is a document written in XML. The document describes a Web service. It specifies the location of the service and the operations (or methods) the service exposes.

The main structure of a WSDL document looks like this:

<definitions>
<types>
  definition of types........
</types>
<message>
  definition of a message....
</message>
<portType>
  definition of a port.......
</portType>
<binding>
  definition of a binding....
</binding>
</definitions>

WSDL Types

The <types> element defines the data types that are used by the web service.
For maximum platform neutrality, WSDL uses XML Schema syntax to define data types.

WSDL Messages

The <message> element defines the data elements of an operation. Each message can consist of one or more parts. The parts can be compared to the parameters of a function call in a traditional programming language.

WSDL Ports

The <portType> element is the most important WSDL element. It describes a web service, the operations that can be performed, and the messages that are involved. The <portType> element can be compared to a function library (or a module, or a class) in a traditional programming language.

WSDL Bindings

The <binding> element defines the message format and protocol details for each port.The binding element has two attributes - name and type.
The name attribute defines the name of the binding, and the type attribute points to the port for the binding.

Conclusion:

WSDL stands for Web Services Description Language
WSDL is written in XML
WSDL is an XML document
WSDL is used to describe Web services
WSDL is also used to locate Web services
WSDL is a W3C recommendation