Abstract: A transaction based constraint enforcer for a database system is arranged to delay constraint checks until the end of a transaction by creating a check stack during the course of the transaction and executing entries on the check stack at the end of the transaction. A stack maker module is arranged for creating and updating said check stack. The stack maker module is operatively connected to a runtime module in the database system and arranged to receive data from said runtime module. An enforcer module is arranged to receive check data from the check stack, to process the check data received from the check stack, and to provide resulting data to the runtime module. The invention also relates to a method for enforcing a set of constraints that governs the integrity of information stored in a database system, and a database system which includes the constraint enforcer.