Creating web services with SWI-Prolog is a breeze. This how-to is intended as your first bluffer's guide. All examples come with fully operational source code.
Deploying Prolog-based web servers
Here is a tutorial with exercises by Anne Ogborn.
We have two servers available with complete source. One is the server that runs http://www.swi-prolog.org, which can be downloaded through GIT from the repository plweb.git. The other is ClioPatria. Although ClioPatria targets semantic web (RDF) applications, it is also useful as a starting point for general purpose web servers.
Here is a very incomplete selection of functionality that you can find in these servers: