7.7 Active Databases
The DBMS has more powerful means of ensuring integrity in a database than column and table constraints. An active database is one in which the DBMS monitors the contents to prevent illegal states from occurring, using constraints and triggers.
7.7.1 Enabling and Disabling Constraints
Column and table constraints are specified when the table is created, and they are checked whenever a change is made to the database to ensure that the new state is a valid one. Changes that could result in invalid states include insertion, deletion, and updating of records. Therefore, the constraints are checked by the DBMS whenever one of these operations is performed, usually for each SQL INSERT, DELETE, or UPDATE statement. This is called ...
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