Telephone directory example

Suppose that you create a database for a personal telephone directory. The database model must record the names, addresses, and telephone numbers of people and organizations that the user requires.

First define the entities. Look carefully at a page from a telephone directory to identify the entities that it contains. The following figure shows a sample page from a telephone directory.

Figure 1. Partial page from a telephone directory

The physical form of the existing data can be misleading. Do not let the layout of pages and entries in the telephone directory mislead you into trying to specify an entity that represents one entry in the book: an alphabetized record with fields for name, number, and address. You want to model the data, not the medium.