Welcome to Jessica
Jessica is a means of combining content repositories and RDF. On the one hand, industries need content management systems that, at their core, is a repository. On the other, they require robust metadata, properly structured, managed and accessible.
Jessica puts the two together. It is an implementation of JSR 170 that sits on top of a vendor-specific RDF store, in the same way as connector architecture has been implemented for commercial repositories to expose the same API. If you use Jena or Sesame, for example, you can turn the metadata it stores into "content", using Jessica.
This extends the advantage that JSR 170 already provides for "classic" repositories, in that systems that use one of the array of RDF stores can convert and expose that information through the JCR API. It also provides the RDF query language that is supported by the RDF store (or implements one), and provides this through the JCR's Query API. So JCR would be able to provide SPARQL, RDQL, etc. alongside the standard XPath.
This is a new project, and is still in its initial planning stage. The project has a blog for more up-to-date information about the status of Jessica.
