UML communication diagrams, formerly known as collaboration diagrams, are used to explore the dynamic nature of your software. Communication diagrams show the message flow between objects in an object-oriented application, and also imply the basic associations (relationships) between classes. Communication diagrams are often used to

1. ■ provide a bird's-eye view of a collection of collaborating objects, particularly within a real-time environment;

2. ■ provide an alternate view to UML sequence diagrams;

3. ■ allocate functionality to classes by exploring the behavioral aspects of a system;

4. ■ model the logic of the implementation of a complex operation, particularly one that interacts with a large number of other objects;

5. ■ explore the roles that objects take within a system, as well as the different relationships in which they are involved when in those roles.

General Guidelines

Create Instance-Level Diagrams to Explore Object Design Issues

Instance-level UML communication diagrams, such as the one shown in Figure 33, depict interactions between objects (instances). Instance-level diagrams are typically created to explore the internal design of object-oriented software. This by far is the most common style of UML communication diagram.

Create Specification-Level Diagrams to Explore Roles

Specification-level UML communication diagrams, such as the one shown in Figure 37, are used to analyze and explore the roles taken by domain classes within a system. This style of UML communication diagram is not common because most modelers identify roles via UML class diagrams.

Apply Robustness Diagram Visual Stereotypes

Figure 33 is effectively a detailed robustness diagram (Jacobson, Christerson, Jonsson, and Overgaard 1992; Rosenberg and Scott 1999).