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Integrity constraints should not
be violated by the update operations. Several update operations may have to be
grouped together. Updates may propagate to cause other updates automatically.
This may be necessary to maintain integrity constraints. In case of integrity
violation, several actions can be taken:
1. Cancel the operation that
causes the violation (REJECT option)
2. Perform the operation but
inform the user of the violation
3. Trigger additional updates so
the violation is corrected (CASCADE option, SET NULL option)
4. Execute a user-specified error-correction routine
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