Chapter 16

Interaction Overview Diagrams

Interaction overview diagrams are a grafting together of activity diagrams and sequence diagrams. You can think of interaction overview diagrams either as activity diagrams in which the activities are replaced by little sequence diagrams, or as a sequence diagram broken up with activity diagram notation used to show control flow. Either way, they make a bit of an odd mixture.

Figure 16.1 shows a simple example of one; the notation is familiar from what you’ve already seen in the activity diagram and sequence diagram chapters. In this diagram, we want to produce and format an order summary report. If the customer is external, we get the information from XML; if internal, we get it from a database. Small sequence diagrams show the two alternatives. Once we get the data, we format the report; in this case, we don’t show the sequence diagram but simply reference it with a reference interaction frame.

When to Use Interaction Overview Diagrams

These are new for UML 2, and it’s too early to get much sense of how well they will work out in practice. I’m not keen on them, as I think that they mix two styles that don’t really mix that well. Either draw an activity diagram or use a sequence diagram, depending on what better serves your purpose.