Persistent objects stored/retrieved by business layer.
At this level we avoid dependance on specific persistence engines
(e.g. Hibernate). We do this by using an interface named
{@link org.apache.roller.business.PersistenceStrategy PersistenceStrategy}
to store, retrieve and remove
{@link org.apache.roller.pojos.PersistentObject PersistentObjects}.
The diagram below shows the objects in the Roller data model and the
relationships between them.