JAX-RS deals with the mapping of java objects to a representation format - any format. Writing a good format, though, is at least as tricky as building RESTful services. So JAX-RS solves only half the problem. What is needed is to make it easy to serialize any object in a manner that scales to the web. For this we have RDF, the Resource Description Framework. By combining JAX-RS and the So(m)mer's @rdf annotation one can remove remove the hurdle of having to create yet another format, and do this in a way that should be really easy to understand.
This is very cool, if a little verbose due to Java syntax.