In order to maintain referential integrity, you'll need to further configure the the database schema (using database admin tools), adding the required foreign keys and rules to enforce it. You'll need to consult the database documentation for exact details on how to do it.
If you're using the bundled dbms (hsqldb), see this thread for some pointers on how to configure it.
Depending on the scope of configuration made to the schema, you may also need to add the appropriate update/delete processes in your modeling.
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