JPA (Java Persistence API) and Java Data Objects (JDO) are two specifications for storing java objects in databases. If JPA is concentrated only on relational databases, then JDO is a more general specification that describes the ORM for any possible bases and repositories.
In principle, JPA can be viewed as part of the JDO specification specialized in relational databases, even though the API of these two specifications does not completely match. The “developers” of specifications also differ – if JPA is developed as JSR, then JDO was first developed as JSR, now it is developed as an Apache JDO project.
