JPA/EJB3 Relationship

Answer 1

Yes, and JPA1 and JPA2 is also implemented by DataNucleus which also implements JDO1, JDO2, JDO3, as well as the OGC Simple Feature spec; and is also the only truly independent implementation (not tied to a large software vendor). Obviously, users are free to slot in whichever JPA implementation they wish into their EJB3 environment

Answer 2

Yes, I had too google OpenJPA but this is correct

Answer 3

The Java Persistence API introduced in Java EE 5 is a subset of EJB 3 and replaces the persistence solution of EJB 2.0 CMP. JPA 1.0 has been defined as part of the EJB 3.0 specification (JSR 220) but can be used without and outside an EJB container. In Java EE 6, JPA 2.0 has its separate specification (JSR 317), outside the EJB 3.1 specification (JSR 318). So to summarize:

• JPA is a subset of EJB 3 and implementations are provided by persistence providers like Toplink Essentials / EclipseLink, Hibernate, Kodo / OpenJPA (Kodo is the project from which the OpenJPA source code was derived and Kodo is now, in turn, based on OpenJPA), etc.

• EJB 3 is a wider specification and implementations are provided by the EJB container of application servers that rely on persistence providers:

  • The default persistence provider of GlassFish v3 is EclipseLink
  • The default persistence provider of JBoss is Hibernate
  • The default persistence provider of WebLogic 10.3.1+ is OpenJPA/Kodo or EclipseLink
  • The default persistence provider of WebSphere 6.1+ is (based on) OpenJPA

Answer 4

You may please refer to the following link, and do let me know if it really helped http://freejavaclass.com/articles/j2ee/ejb/ejb3_relationship_types.jsp