"SSDL is a SOAP-centric description language for Web Services. It promotes message-orientation as the architectural paradigm for building distributed applications and enables protocol-based integration between Web Services. The SSDL effort is an attempt to explore ideas in the areas of contract and protocol description and Web Services implementations using message-oriented programming abstractions."
"I collaborated with a small team of people to produce a description language for Web Services that we think is exciting since it encourages us to reason in terms of messages, rather than 'operations', 'interfaces', and 'inheritance', when writing contracts...We have made available four such protocol frameworks: MEP, CSP, Rules, and SC). There are also an SSDL high-level overview document and a whitepaper available."
The SOAP Service Description Language and SSDL: The SOAP Service Description Language.