1. Integrity constraints provide a way of ensuring that changes made to the database by authorized users do not result in a loss of data consistency.

2. We saw a form of integrity constraint with E-R models:

• key declarations: stipulation that certain attributes form a candidate key for the entity set.
• form of a relationship: mapping cardinalities 1-1, 1-many and many-many.

3. An integrity constraint can be any arbitrary predicate applied to the database.

4. They may be costly to evaluate, so we will only consider integrity constraints that can be tested with minimal overhead.