The Activity Diagram

In activity diagrams, UML (Unified Modeling Language) methods are used to describe how a system realizes certain behaviors. Activity diagrams can also be used to clearly depict complex processes. Sequential and parallel processes are illustrated in diagrams as actions, control flows and object flows. Activity diagrams are used, for example, to describe business processes and use cases or for documenting the implementation of system operations.

The diagram can be opened:

• by double-clicking on the diagram

The diagram

The most important editing functions

	Create Action Creates an action. An action is a single procedural step that cannot be refined any further within the overall behavior of an activity. All actions together describe the behavior of an activity and an action is initiated by detailed control or object flows. The same action can be called up multiple times in an activity diagram. An action can invoke further actions or an activity. Individual actions can be refined in an additional activity diagram as needed.
	Create Fork/Join Node Creates a control element to illustrate parallel processes. Clicking the middle of the bar lets you switch between horizontal and vertical forking directions. A fork/join node is a control element that subdivides a process into several parallel processes (splitting) or joins several processes (synchronization). A bar is used to indicate a fork in the diagram.
	Create Decision/Merge Node Creates a control element to visualize alternative processes. Use decision/merge nodes —  the diamond symbol in a diagram — to visualize alternatives and convergences. Alternative processes usually have prerequisite conditions which have to be in place.
	Create Object Node Creates a reference for an object. An object node represents an object to which an action transfers data and for which an action creates or alters data. They can also be used to model different forms of classes, variables, constants or memory of any kind.
	Create Initial Node Creates an entry point for the process of an activity.
	Create Final Node Creates an exit point for the process of an activity. Individual control flows or object flows end at this point.
	Create Flow Final Node Creates an end point for individual processes. An activity ends at this point. A diagram must have at least one end node. If multiple final nodes exist, each leads to the termination of all activities in the diagram.
	Create Object Flow Connects an action or a control element to an object node with a dashed arrow. The arrow head points in the direction of the element that was clicked last. Indicated here by a dashed arrow, the object flow describes the transfer of data to or from an object node.
	Create Control Flow Links one or two actions to a control element with a solid arrow. The arrow head points in the direction of the element that was clicked last. Control flow describes the sequence in which actions occur. They are indicated by a solid arrow in the diagram.
	Create Partition Subdivides the diagram into areas and groups actions. You can change the size of a partition by holding down the mouse key and pulling the window corner. Partitions or swimlanes are used for grouping actions and showing different fields or actors. They are visualized in the diagram by vertical or horizontal areas that are named according to the partition. Partitions can be nested or encapsulated. An action can be a child to multiple partitions.
	Create Note Used to create a note to provide additional information about the chart or chart element.
	Create Note Relationship links a note to another chart element.