Summary of ER (Contd.)
Several kinds of integrity constraints can be expressed in the ER model: key constraints, participation constraints. Some foreign key constraints are also implicit in the definition of a relationship set.
- Some of these constraints can be expressed in SQL only if we use general CHECK constraints or assertions.
- Some constraints (notably, functional dependencies) cannot be expressed in the ER model.
- Constraints play an important role in determining the best database design for an enterprise.