Access Database Design and Programming, Second Edition

Chapter 2. The Entity-Relationship Model of a Database

Let us begin our discussion of database design by looking at an informal database model called the entity-relationship model . This model of a relational database provides a very useful perspective, especially for the purposes of the initial design of the database.

We will illustrate the general principles of this model with our LIBRARY database example, which we will carry through the entire book. This example database is designed to hold data about the books in a certain library. The amount of data we will use will be kept artificially small—just enough to illustrate the concepts. (In fact, at this point, you may want to take a look at the example database. For details on downloading it from the Internet, or on using Microsoft Access to create it yourself, see Appendix D.) In the next chapter, we will actually implement the entity-relationship (E/R) model for our LIBRARY database.

What Is a Database?

A database may be defined as a collection of persistent data. The term persistent is somewhat vague, but is intended to imply that the data has a more-or-less independent existence, or that it is semipermanent. For instance, data that are stored on paper in a filing cabinet, or stored magnetically on a hard disk, CD-ROM, or computer tape are persistent, whereas data stored in a computer’s memory are generally not considered to be persistent. (The term “permanent” is a bit too strong, since very little in life is truly permanent.) ...