When to Use Class Diagrams

Class diagrams are the backbone of nearly all OO methods , so you will find yourself using them all the time. This chapter covers the basic concepts; Chapter 6 discusses many of the advanced concepts.

The trouble with class diagrams is that they are so rich, they can be overwhelming to use. Here are a few tips.

Don't try to use all the notations available to you. Start with the simple stuff in this chapter: classes, associations, attributes, generalization, and constraints. Introduce other notations from Chapter 6 only when you need them.
Fit the perspective from which you are drawing the models to the stage of the project.
- If you are in analysis, draw conceptual models.
- When working with software, concentrate on specification models.
- Draw implementation models only when you are illustrating a particular implementation technique.
Don't draw models for everything; instead, concentrate on the key areas. It is better to have a few diagrams that you use and keep up to date than to have many forgotten, obsolete models.

The biggest danger with class diagrams is that you can get bogged down in implementation details far too early. To combat this, focus on the conceptual and specification perspectives. If you run into these problems, you may well find CRC cards (see page 75) to be extremely useful.