In this chapter, we've looked at modeling and implementing data integrity. Three kinds of integrity constraintsdomain, transition, and entitycontrol individual relations, while referential integrity constraints ensure that the relations between relations are maintained. Finally, database constraints and transaction constraints control the database as a whole.
Data integrity is implemented in the database schema using a combination of declarative and procedural integrity. Declarative integrity is explicitly declared as part of the schema and is the preferred method of implementation. However, not all constraints can be implemented using declarative integrity, and where they cannot, procedural integrity must be used.
In Chapter 5, we'll examine relational algebra and the operations that can be performed on the relations in the database.