Section 3.2. Activities and Actions

3.2. Activities and Actions

Actions are active steps in the completion of a process. An action can be a calculation, such as Calculate Tax, or a task, such as Verify Author's Details.

The word "activity" is often mistakenly used instead of "action" to describe a step in an activity diagram, but they are not the same. An activity is the process being modeled, such as washing a car. An action is a step in the overall activity, such as Lather, Rinse, and Dry.

The actions in this simple car-washing activity are shown in Figure 3-3.

Figure 3-3. Capturing the three actionsLather, Rinse, and Drythat make up washing a car in an activity diagram

In Figure 3-3, the entire activity is enclosed within the rounded rectangle called an activity frame . The activity frame is used to contain an activity's actions and is useful when you want to show more than one activity on the same diagram. Write the name of the activity in the upper left corner.

The activity frame is optional and is often left out of an activity diagram, as shown in the alternative Wash Car activity in Figure 3-4.

Figure 3-4. The activity frame can be omitted

Although you lose the name of the activity being displayed on the diagram itself, it is often more convenient to leave out the activity frame when constructing a simple activity diagram.