Java Persistence/TopLink Essentials
TopLink Essentials is an open source project from the Sun java.net Glassfish community. It is the EJB3 JPA 1.0 reference implementation, and is the JPA provider for the Sun Glassfish v1 application server.
TopLink Essentials was based on the TopLink product, which Oracle contributed some of the source code from to create the TopLink Essentials project. The original contribution was from TopLink's 10.1.3 code base, only some of the TopLink product source code was contributed, which did not include some key enterprise features. The package names were changed and some of the code was moved around.
TopLink Essentials has been replaced by the EclipseLink project. EclipseLink will be the JPA 2.0 reference implementation and be part of Sun Glassfish v3.