SOAP

SOAP is a protocol for exchanging XML-based messages over a computer network, normally using HTTP. SOAP forms the foundation layer of the Web services stack, providing a basic messaging framework that more abstract layers can build on. SOAP can be used to facilitate a Service-Oriented architectural pattern.

Wikipedia (2006). Articles>Information Design>XML>SOAP

XML, REST, and SOAP at Yahoo

Yahoo Search Marketing makes extensive use of XML internally, for data exchange and APIs between back-end systems, and externally, as the primary interaction mechanism with third parties via REST and SOAP APIs.

Darugar, Parand. IDEAlliance (2005). Articles>Information Design>XML>SOAP