Telephone Directory Example

Figure 15 shows the telephone directory example and includes the entities, relationships, and attributes. This diagram includes the relationships that you establish with the matrix. After you study the diagram symbols, compare the E-R diagram in Figure 15 with the matrix in Figure 10. Verify for yourself that the relationships are the same in both figures.

A matrix such as Figure 10 is a useful tool when you first design your model, because when you fill it out, you are forced to think of every possible relationship. However, the same relationships appear in a diagram such as Figure 15, and this type of diagram might be easier to read when you review an existing model.

Figure 15. Preliminary Entity-Relationship Diagram of the Telephone Directory Example

After the Diagram Is Complete

The rest of this chapter describes how to perform the following tasks:

• Translate the entities, relationships, and attributes into relational constructs.
• Resolve the E-R data mode.l
• Normalize the E-R data model.

Implementing a Relational Data Model shows you how to create a database from the E-R data model.