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The State of XML Web Services

In the Userland XML-RPC specification, XML-RPC is used to implement a simple RPC mechanism on top of XML on top of an HTTP post. This specification is complete; you can implement it today, and is guaranteed to work tomorrow.

SOAP, however, is an evolving standard. The syntax is a little different from XML-RPC. As SOAP evolves, more and more extensions have been added onto it. SOAP 1.1 is a w3c recommendation, which means that it is essentially done. SOAP 1.2. is still a moving target, and its extensions are not yet final. Much of the work on these extensions has been spearheaded by Microsoft and IBM.

In addition, SOAP includes a header, which can contain additional information for SOAP extensions; these extensions can be anything that a service vendor might want to specify.

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