Integrity Constraints (ICs)
IC: condition that must be true for any instance of the database; e.g., domain constraints.
- ICs are specified when schema is defined.
- ICs are checked when relations are modified.
A legal instance of a relation is one that satisfies all specified ICs.
- DBMS should not allow illegal instances.
If the DBMS checks ICs, stored data is more faithful to real-world meaning.
- Avoids many data entry errors, too!