Overview

Extensible Markup Language (XML) is what makes Web services possible. Everything to do with today s Web services are based, one way or another, on XML. The link between XML and Web services is inextricable and incontrovertible. All data transfer to or from a Web service always has to be in the form of an XML document. That is a given. The input parameters to a Web service are thus structured and defined using XML, as is the output generated by a Web service. In addition, the input/output operations of a Web service, which are implemented in the form of a remote procedure call mechanism, are realized using an XML-based messaging scheme namely, SOAP.

The workings of a Web service are also described using XML, in this case WSDL, which is an XML derivative. The W3C s proposed definition of what a Web service is supposed to be states categorically, in the very first sentence, no less, that the public interfaces and bindings of a Web service are defined and described using XML. Many of the auxiliary standards associated with Web services (as shown in Table 1.1), such as those related to security and discovery (e.g., WS-Inspection), also happen to be XML-centric. Even the proposed GUI standard for Web services (i.e., WSRP), though not XML-specific, given that information presentation per se is not exactly XML s cup of tea, still makes sure that it includes support for presentation-oriented dialects of XML, such...