The current WSDL standard operates at the syntactic level and lacks the semantic expressivity needed to represent the requirements and capabilities of Web Services. This 'Web Service Semantics' technical note defines a mechanism to associate semantic annotations with Web services that are described using WSDL. It is conceptually based on, but is a significant refinement in details of, the original WSDL-S proposal from the LSDIS laboratory at the University of Georgia. In this proposal, we assume that formal semantic models relevant to the services already exist. In our approach, these models are maintained outside of WSDL documents and are referenced from the WSDL document via WSDL extensibility elements. The type of semantic information that would be useful in describing a Web Service encompass the concepts defined by the semantic Web community in OWL-S and other efforts (e.g., METEOR-S, and WSMO). The semantic information specified in this document includes definitions of the precondition, input, output and effects of Web service operations.

http://lsdis.cs.uga.edu/library/download/WSDL-S-V1.pdf