One of my data models use natural keys that can change overtime. How are foreign keys and cascades implemented in the latest version of Firebird? Is it like in a REAL rdbms where the foreign key is actually a internal pointer to the referenced table and cascades are "instant" no matter how big the database is OR is it a fake dbms where the foreign key is duplicated on all referencing tables and massive cascades will cause all sorts of locks and crash the dbms?