Database Design

Database systems are designed to manage large bodies of information. These large bodies of information do not exist in isolation. They are part of the operation of some enterprise whose end product may be information from the database or may be some device or service for which the database plays only a supporting role.

The first two chapters of this part focus on the design of database schemas. The entity-relationship (E-R) model described in Chapter 7 is a high-level data model. Instead of representing all data in tables, it distinguishes between basic objects, called entities, and relationships among these objects. It is often used as a first step in database-schema design.

Relational database design—the design of the relational schema— was covered informally in earlier chapters. There are, however, principles that can be used to distinguish good database designs from bad ones. These are formalized by means of several “normal forms” that offer different trade-offs between the possibility of inconsistencies and the efficiency of certain queries. Chapter 8 describes the formal design of relational schemas.

The design of a complete database application environment that meets the needs of the enterprise being modeled requires attention to a broader set of issues, many of which are covered in Chapter 9. This chapter first covers the design of Web-based interfaces to applications. The chapter then describes how large applications are architected using multiple layers of abstraction. Finally, the chapter provides a detailed discussion of security at the application and database levels.