Interaction overview diagrams are new to UML 2. They are a variant of an activity diagram where each bubble on the diagram represents another interaction diagram. UML interaction overview diagrams are used to

1. ■ overview the flow of control within a business process;

2. ■ overview the detailed logic of a software process;

3. ■ connect several diagrams together.

Figure 55 depicts an interaction overview diagram that models how the logic for enrolling in a seminar could be implemented.

Reference Other Diagrams, Don't Depict Them

Although it is very interesting to depict a diagram within another diagram, as you see with the two diagram frames in Figure 55, the reality is that you rarely have the drawing space to do such a thing. A more realistic version of the diagram is presented in Figure 56 that uses just interaction use frames to refer to operations implemented by various objects.

Don't List Lifelines

Both Figure 55 and Figure 56 list the lifelines that appear within the frame—Figure 56 lists only two because it doesn't depict as much detail as Figure 55. In either case the information is superfluous; you can gain it from looking at the diagram.