What is WSDL?
WSDL is a language for describing the capabilities of Web services. Proposed by IBM and Microsoft, WSDL combines the best of IBMs NASSL (Network Accessible Services Language) and Microsoft SOAP Contract Language. WSDL is based on XML and is a key part of the UDDI initiative. The WSDL document specification helps improve interoperability between applications, regardless of the protocol or the encoding scheme. The WSDL 1.1 specification defines WSDL as an XML grammar for describing network services as collections of communication endpoints capable of exchanging messages.
Essentially, a WSDL document describes how to invoke a service and provides information on the data being exchanged, the sequence of messages for an operation, protocol bindings, and the location of the service. A WSDL document defines services as a collection of endpoints, but separates the abstract definition from the concrete implementation. Messages and port types provide abstract definitions for the data being exchanged and the operations being performed by a service. A binding is provided to map to a concrete set of ports, usually consisting of a URL location and a SOAP binding.