UML activity diagrams

In UML, an activity diagram provides a view of the behavior of a system by describing the sequence of actions in a process. Activity diagrams are similar to flowcharts because they show the flow between the actions in an activity; however, activity diagrams can also show parallel or concurrent flows and alternate flows.

In activity diagrams, you use activity nodes and activity edges to model the flow of control and data between actions.

Activity diagrams are helpful in the following phases of a project:

Before starting a project, you can create activity diagrams to model the most important workflows.
During the requirements phase, you can create activity diagrams to illustrate the flow of events that the use cases describe.
During the analysis and design phases, you can use activity diagrams to help define the behavior of operations.

As the following figure illustrates, an activity diagram belongs to an activity in the model. When you create an activity diagram, it is displayed in the Project Explorer view in the Diagrams folder, and also in the Models folder as a child element of the owning activity. The corresponding activity frame is displayed in the diagram editor.

The header of the activity frame displays the name of the activity, Activity1, and the body of the activity frame displays the nodes and edges that describe the activity. After you create the activity diagram, you cannot move it in the Project Explorer view.

An activity diagram in the Project Explorer and in the diagram editor

The following topics describe model elements in activity diagrams: