The Unified Modeling Language User Guide SECOND EDITION [Electronic resources] نسخه متنی

Chapter 5. Relationships

In this chapter

• Dependency, generalization, and association relationships

• Modeling simple dependencies

• Modeling single inheritance

• Modeling structural relationships

• Creating webs of relationships

When you build abstractions, you'll discover that very few of your classes stand alone. Instead, most of them collaborate with others in a number of ways. Therefore, when you model a system, not only must you identify the things that form the vocabulary of your system, you must also model how these things stand in relation to one another.

In object-oriented modeling, there are three kinds of relationships that are especially important:

dependencies , which represent using relationships among classes (including refinement, trace, and bind relationships); generalizations, which link generalized classes to their specializations; and associations, which represent structural relationships among objects. Each of these relationships provides a different way of combining your abstractions.

Building webs of relationships is not unlike creating a balanced distribution of responsibilities among your classes. Over-engineer, and you'll end up with a tangled mess of relationships that make your model incomprehensible; under-engineer, and you'll have missed a lot of the richness of your system embodied in the way things collaborate.