Figure uml.07 an example of a UML Ativity Diagram.
You use activity diagrams to model the dynamic aspects of a system. For the most part, this involves modeling the sequential (and possibly concurrent) steps in a computational process. With an activity diagram, you can also model the flow of values among steps. Activity diagrams may stand alone to visualize, specify, construct, and document the dynamics of a society of objects, or they may be used to model the flow of control of an operation. Whereas interaction diagrams emphasize the flow of control from object to object, activity diagrams emphasize the flow of control from step to step.
An activity is an ongoing structured execution of a behavior. The execution of an activity ultimately expands into the execution of individual actions, each of which may change the state of the system or communicate messages. For example, Figure uml.07 is an activity diagram representing activities related to managing an Incident. Rounded rectangles represent activities; arrows between activities represent control flow; thick bars represent the synchronization of the control flow.
The activity diagram of Figure uml.07 depicts that the AllocateResources, CoordinateResources, and DocumentIncident can be initiated only after the OpenIncident activity has been completed. Similarly, the ArchiveIncident activity can be initiated only after the completion of AllocateResources, CoordinateResources, and DocumentIncident. These latter three activities, however, can occur concurrently.