12.4. Entity EJBs and nonflat data structures
A ‘flat’ data structure is one in which the all the relevant entities are collated into one searchable unit, such as a single database table or a single directory suffix. In many applications, the underlying data structure is not flat; it may be that a given EJB models data in different database tables, or even in different data sources.
When using bean-managed persistence, there is no reason why an entity EJB’s data should not be drawn from a number of different database tables. Indeed, a prominent advantage of entity EJBs is that they can provide a simple, object-oriented view of a complex underlying data model. All that is necessary is that the developer have a sufficiently good grasp of SQL to ...
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