IEEE Article on Jena

Jena: A Semantic Web Toolkit: " The Jena download contains three implementations of the API: One stores its data in main memory, another stores its data in a relational database, and a third uses Sleepycat Software's open-source embedded database, Berkeley DB (www.sleepycat.com/). A system programming interface makes it easy to introduce new stores...The Berkeley DB store, like the relational store, is persistent. While it lacks the transaction support of the relational database, it is up to an order of magnitude faster than some relational databases." Also notes they're working on a RDF-S and DAML APIs.