CHAPTER 4

Learning from the Data Model

In the previous chapter, we attempted to extract the essential tasks involved in a real-world problem and express them with use cases. We also made a first attempt at determining the data that is necessary to support those tasks and formed an initial data model, which we depicted with a class diagram. In this chapter, we look more closely at the data model to see how it can further our understanding of a database system.

A data model is a precise description of the data stored for a real-world problem, in much the same way that a mathematical equation describes a real-world physical event, or an architectural drawing describes the plan of a building. However, like a mathematical equation or an architectural plan, the data model is not a complete nor exact description of a real situation. It will always be based on definitions and assumptions, and it has a finite scope. For example, a high school student's simple mathematical equation to describe the path of a ball tossed into the air will probably make assumptions about the constancy of the gravitational force and the absence of air resistance, and will likely assume low speeds where relativistic effects c....