3. The SOAP Protocol

THE WEB SERVICES ARCHITECTURE GROUP AT THE W3C has defined a Web service as follows (italics added):

A Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP-messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.

Although our definition (see Chapter 1, “Web Services Overview and Service-Oriented Architectures”) may be a bit broader, it’s clear that SOAP is at the core of any survey of Web service technology. So just what is SOAP, ...

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