David Booth, a W3C Fellow, has a picture which I've seen in several talks and wanted to document. The picture shows how a web services description (WSD) is referenced by the client and the server, but, more importantly, how it references semantics. XML semantics has been something of a pet peeve of mine in the past. Here's the picture:
The point that David makes is that the server and the client have to agree on semantics. If they don't, of course, the result is gibberish. The semantics might be in some formal langauge, although not very many people enjoy writing formal semantics of anything. I used to do this; its very time consuming. More likely, the semantics is just in written in English. David wants the semantics to be written and referenced by the WSD so that it can be found and used by the programmer. I think this is an excellent idea. Even a natural language semantics would be very helpful in understanding the WSD and applying it.
David suggests using the "targetNamespace" attribute in WSDL for the reference. I have no idea whether that's a good idea or not. I do know that other people have other ideas about what that attribute should be used for.