ozone is a fully featured, object-oriented database management system completely implemented in Java and distributed under an open source license. The ozone project aims to evolve a database system that allows developers to build pure object-oriented, pure Java database applications. Just program your Java objects and let them run in a transactional database environment.
ozone includes a fully W3C compliant DOM implementation that allows you to store XML data. You can use any XML tool to provide and access these data. Support classes for Apache Xerces-J and Xalan-J are included.
Besides the native API, ozone provides a ODMG 3.0 interface. Although not fully ODMG compliant it helps you to port applications to/from ozone.
ozone does not depend on any back-end database or mapping technology to actually save objects. It contains its own clustered storage and cache system to handle persistent Java objects.URL: http://www.ozone-db.org/frames/home/what.html