Activity Diagram

Activity diagrams are graphical representations of workflows. They primarily show the overall flow of control, but they can also include elements showing the flow of data.

The complete workflow in a diagram is called an activity.

Diagram Model

Name	Graphical Representation	Description
Entry and Exit		The activity starts at the entry point. It is required to define the initiating control event. Please note, that there must be at most one start node in an activity. The exit node ends the activity. Avoid multiple end nodes, but in some cases multiple end nodes can make a diagram more readable. Adding a label to the exit node is optional.
Action		Element in the control flow that requires an active resource (e.g. CPU) to create some type of results (e.g. output data, event); must have at least a control flow input and output. Merge actions as far as possible to reduce complexity (abstraction). Do not mix non-safety/non-security related and safety/security related actions in one element.
Activity		This element refers to another activity diagram. Splitting the content into several diagrams can help to reduce the complexity and avoid repetitions.
Decision		A decision has always one input control flow and several output control flows. The decision is usually phrased as a question.
Events		Events can be sent and received in the same or in different diagrams.
Fork and Join		Forks and joins are used to model asynchronous behaviour.

Example