Summary

In this chapter, we've examined the relationships between entities in detail. We've looked at each type of binary relationship—one-to-one, one-to-many, and many-to-many—and seen how to represent them in the data model by establishing a primary relation and including its candidate key in the other relationship participant, the foreign relation. In addition, we've examined the special cases of unary and ternary relationships and seen how they can also be represented in the data model.

You've now seen all the basic components of a data model: the entities, their attributes, and the relationships between them. In Chapter 4, we'll turn to data integrity and the mechanisms available to you to maintain the consistency of the database.