The Java EE 6 Tutorial, Volume I

The Table per Concrete Class Strategy

In this strategy, which corresponds to InheritanceType.TABLE_PER_CLASS, each concrete class is mapped to a separate table in the database. All fields or properties in the class, including inherited fields or properties, are mapped to columns in the class’s table in the database.

This strategy provides poor support for polymorphic relationships, and usually requires either SQL UNION queries or separate SQL queries for each subclass for queries that cover the entire entity class hierarchy.

Support for this strategy is optional, and may not be supported by all Java Persistence API providers. The default Java Persistence API provider in the Enterprise Server does not support this strategy.