Apache ObJectRelationalBridge (OJB) is an Object/Relational mapping tool that allows transparent persistence for Java Objects against relational databases.
OJB has been designed for a large range of applications, from embedded systems to rich client application to multi-tier J2EE based architectures.
Functionality
OJB uses an XML based Object/Relational mapping. The mapping resides in a dynamic MetaData layer, which can be manipulated at runtime through a simple Meta-Object-Protocol (MOP) to change the behaviour of the persistence kernel.
Further studies.
www.Apache.org [1]