A decision involves selecting one control-flow transition out of many control-flow transitions based upon a condition. For example, once a report is printed by the project management system, other reports may be selected and printed if the project manager chooses to print more reports.
In the UML, a decision is shown as a diamond shape with incoming control-flow transitions and outgoing control-flow transitions where each outgoing control-flow transition is labeled with a guard condition in square brackets indicating the condition that must be satisfied for the transition to fire, or occur. Figure 8-7 shows that once a report is printed, a project manager may choose to print more reports. Notice that because the diamond shape is in the project manager's swimlane, the project manager is responsible for making the decision.