JDO provides a means of transparent persistence of objects of user defined classes. With JDO there are actually 3 types of classes.

• Persistence Capable classes are classes whose instances can be persisted to a datastore. JDO provide the mechanism for persisting these instances, and they are core to JDO. These classes need to be enhanced according to a JDO Meta-Data specification before use within a JDO environment.
• Persistence Aware classes are classes that manipulate Persistence Capable instances through direct attribute manipulation. These classes are typically enhanced with very minimal JDO Meta-Data. The enhancement process performs very little changes to these classes.
• Normal classes are classes that aren't themselves persistable, and have no knowledge of persistence either. These classes are totally unchanged in JDO, and require no JDO Meta-Data whatsoever.