As stated at the beginning of this chapter, Web Services are based on the exchange of messages using non-proprietary protocol messages. The messages themselves are not sufficient to define the Web Service platform. We actually need a list of standard components, including the following:
A language used to define the interfaces provided by a Web Service, in a manner that is not dependent on the platform on which it is running or the programming language used to implement it
A common standard format for exchanging messages between Web Service Producers and Web Service Consumers
A registry within which the service definitions can be placed
The Web Service Description Language , that is, WSDL (http://www.w3.org/TR/wsdl) is the de facto standard for providing a description of the Web Service contract exposed to clients. In particular, a WSDL document describes a Web Service in terms of the operations that it provides and the data types that each operation requires as inputs and...