When to Use Class Diagrams

Class diagrams are the backbone of the UML, so you will find yourself using them all the time. This chapter covers the basic concepts; Chapter 5 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 5 only when you need them.

• I've found conceptual class diagrams very useful in exploring the language of a business. For this to work, you have to work hard on keeping software out of the discussion and keeping the notation very simple.

• 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 focus exclusively on structure and ignore behavior. Therefore, when drawing class diagrams to understand software, always do them in conjunction with some form of behavioral technique. If you're going well, you'll find yourself swapping between the techniques frequently.