Why Build a Data Model
You already have some idea regarding the type of data in your database and how that data needs to be organized. This is the beginning of a data model. By using some type of formal notation to build your data model, you can help your design in two ways:
A mental model often contains unexamined assumptions; formalizing the design reveals these points.
A formal statement makes the model explicit, so that others can return comments and suggestions in the same form.
Entity-Relationship Data-Model Overview
Different books present different formal methods of modeling data. Most methods force you to be thorough and precise. If you have already learned a method, by all means use it.
This chapter presents a summary of the entity-relationship (E-R) data model, a modeling method taught in training courses presented by Informix. The
E-R modeling method uses the following steps:
1. Identify and define the principal data objects (entities, relationships, and attributes).
2. Diagram the data objects using the entity-relationship approach.
3. Translate your entity-relationship data objects into relational constructs.
4. Resolve the logical data model.
5. Normalize the logical data model.
Steps 1 through 5 are discussed in this chapter. Chapter 9, "Implementing Your Data Model," discusses the final step of converting your logical data model to a physical schema.
The end product of data modeling is a fully defined database design encoded in a diagram similar to Figure 8-21, which shows the final set of tables for a personal telephone directory. The personal telephone directory is an example developed in this chapter. It is used rather than the stores7 database because it is small enough to be developed completely in one chapter but large enough to show the entire method.
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