I'm an RDF and Semantic Web person, not a Web Services person. I tried hard to ignore Web Services until two months ago. Hugo, Yves, and others will certainly know things here that I don't. My goal is to advance team-wide understanding of the web services architecture, the RDF architecture, and the areas of conflict and possible cooperation between them.
Technically, it's not very interesting. It's an extensible and flexible message-passing system, usually envisioned as Remote Procedure Calls with XML-encoded parameters, carried on an HTTP POST. It's web forms being filled out by computers. The basic element is XML-RPC which was first implemented in April 1998.
RPC's have been around for 25 years. RFC 1057 documents one open and widely deployed standard. Web Services differ from previous RPC systems in two main ways:
The Web Services Architecture currently involves three components (layered on existing W3C Recommendations):
Technically, it's not very interesting. It's an extensible and flexible knowledge representation system, usually envisioned as web pages containing XML which states the properties of things.
One of the earliest use cases in communication: a group of us want food, but we don't know where to find it. We send out scouts looking for it. One of them finds it. How does the scout tell us where it is?