However, since it is unreasonable to expect a single type system grammar to be used to describe all message formats present and future, WSDL allows using other type definition languages via extensibility.
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 (services).
WSDL addresses this need by defining an XML grammar for describing network services as collections of communication endpoints capable of exchanging messages.
WSDL service definitions provide documentation for distributed systems and serve as a recipe for automating the details involved in applications communication.
It is important to observe that WSDL does not introduce a new type definition language.