Developing a Data Model

Abstract

In the previous chapters, you've seen how to determine the requirements of a database problem by considering the tasks users of the system need to carry out. Tasks were represented with use cases, and a simple data model was developed to represent the required data. In Chapter 4, you saw that a great deal can be learned about a problem by questioning some of the details of simple relationships, particularly the number of objects involved at each end of a relationship. In this chapter, you'll be introduced to a few problems that frequently occur in order to enlarge your armory for attacking tricky situations. Attribute, Class, or Relationship? It is never possible to say that a given data model is the correct one. We can only say that it meets the requirements of a problem within a given scope, and subject to certain assumptions or approximations. If we have a piece of data describing some person or thing or event, it is possible that there may be different ways of representing that information. In this section, we look at a simple problem, described in Example 5-1, for which various pieces of data may be represented as an attribute, class, or relationship depending on the overall requirements of the problem.