Overview

SOAP is currently a fundamental, prerequisite building block for XML Web services. SOAP is used to send input to and receive output from conventional XML Web services. Thus, it is the underlying communications mechanism for today s Web services. Since a Web service requires input parameters in order to be activated, SOAP is also considered to be what invokes a Web service because it delivers the input parameters.

The role and scope of SOAP, however, are not limited to Web services. SOAP is the latest in a long line of distributed computing initiatives, which in this context include CORBA and Microsoft s COM/DCOM, though it is not meant to totally displace either of these powerful, object-oriented methodologies. SOAP sets out to be a simpler alternative that does not provide all the high-end bells and whistles (e.g., automatic garbage collection).

SOAP is totally XML-centric. SOAP is a messaging scheme that works by exchanging XML documents. It is formally characterized as a lightweight communications protocol for exchanging XML-based information between applications in a decentralized, distributed environment like the Web. In the interests of putting a stake in the ground, think of SOAP, to begin with, as an XML datagram.

XML, as should now be abundantly clear, is a mechanism for describing the meaning and context of data albeit based on both sides (i.e., creator and subsequent reader or consumer) being privy to some common intelligence (e.g., XML schema or DTD). XML s initial...