The static model addresses the static structural view of a problem, which does not vary with time. A static model describes the static structure of the system being modeled, which is considered less likely to change than the functions of the system. In particular, a static model defines the classes in the system, the attributes of the classes, the relationships between classes, and the operations of each class. In this chapter, static modeling refers to the modeling process and the UML class diagram notation is used to depict the static model.

The concepts of objects, classes, and class attributes are described in Chapter 4. This chapter describes the relationships between classes. Three types of relationships are described: associations, whole/part (composition and aggregation) relationships, and generalization/specialization (inheritance) relationships. In addition, this chapter addresses special considerations in static modeling of the problem domain, including static modeling of the total system context and software system context, as well as static modeling of entity classes. Design of class operations is deferred to the design phase, and is addressed during class design, as described in Chapter 14.

Static models are depicted on class diagrams, as described in this chapter. Section 7.1 describes the different kinds of associations between classes. Section 7.2 describes whole/part relationships, particularly composition and aggregation hierarchies. Section 7.3 describes generalization/specialization hierarchies. Section 7.4 provides an overview of constraints. Section 7.5 describes static modeling with UML, in which the initial emphasis is on modeling the physical classes and entity classes.