Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and the Unified Process, Second Edition

27.5. Roles as Concepts vs. Roles in Associations

In a domain model, a real-world role—especially a human role—may be modeled in a number of ways, such as a discrete concept, or expressed as a role in an association.^[2] For example, the role of cashier and manager may be expressed in at least the two ways illustrated in Figure 27.11.

^[2] For simplicity, other excellent solutions such as those discussed in [Fowler96] are ignored.

Figure 27.11. Two ways to model human roles.

The first approach may be called “roles in associations”; the second “roles as concepts.” Both approaches have advantages.

Roles in associations are appealing because they are ...