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Activity Diagram

Activity diagrams are used to model system behaviors, and the way in which these behaviors are related in an overall flow of the system (that is, dynamic element interactions). The logical paths a process follows, based on various conditions, concurrent processing, data access, interruptions and other logical path distinctions, are all used to construct a process, system or procedure.

You generate Activity diagram elements and connectors from the 'Activity' pages of the Diagram Toolbox.

Example Diagram

This diagram illustrates some of the features of Activity diagrams, including Activities, Actions, Start Nodes, End Nodes and Decision points.

Activity Diagram Element Toolbox Icons



See also

Activity element

An Activity element organizes and specifies the participation of subordinate behaviors, such as sub-Activities or Actions, to reflect the control and data flow of a process.



An Action element describes a basic process or transformation that occurs within a system, and is the basic functional unit within an Activity diagram.

Partition element

A Partition element is used to logically organize an Activity's elements.

Send element

The Send element depicts the action of sending a signal, in an Activity diagram.

Receive element

A Receive element defines the acceptance or receipt of a request, in an Activity diagram.

Sub-Activity element

A Structured Activity is an activity node that can have subordinate nodes as an independent Activity Group.

Structured Activity
Region element

Enterprise Architect supports two types of Region element: Expansion Regions and Interruptible Activity Regions.

An Expansion Region surrounds a process to be imposed multiple times on the incoming data, once for every element in the input collection.

An Interruptible Activity Region surrounds a group of Activity elements, all affected by certain interrupts in such a way that all tokens passing within the region are terminated should the interruption(s) be raised.

Region Expansion Region
Exception element

The Exception Handler element defines the group of operations to carry out when an exception occurs.


An Activity Parameter Node accepts input to an Activity or provides output from an Activity.

Activity Parameter Nodes
Object element

An Object is a particular instance of a Class at run time.

Central Buffer Node element

A Central Buffer Node is an object node for managing flows from multiple sources and destinations, represented in an Activity diagram.

Central Buffer Node
Data Store element

A Datastore defines permanently stored data.


An Expansion Node is a shorthand notation to indicate that the Action/Activity consists of an Expansion Region.

Expansion Node
Initial element

An Initial element is used to define the start of a flow when an Activity is invoked.

Decision element

In an Activity diagram or Interaction Overview diagram, a Decision indicates a point of conditional progression: if a condition is True, then processing continues one way; if not, then another.

A Merge Node for UML Activity diagrams as used in Sparx Systems Enterprise Architect models.

A Merge Node brings together a number of alternative flow paths in Activity, Analysis and Interaction Overview diagrams.

Synchronize element

A Synch state is useful for indicating that concurrent paths of a StateMachine are synchronized. It is used to split and rejoin periods of parallel processing.


A Fork/Join element can be used to:

1)  Split a single flow into a number of concurrent flows

2)  Join a number of concurrent flows or

3)  Both join and fork a number of incoming flows to a number of outgoing flows

Fork/Join Fork Join
Flow Final element

The Flow Final element depicts an exit from the system, as opposed to the Activity Final, which represents the completion of the Activity.

Flow Final
Final element

The Activity Final element indicates the completion of an Activity; upon reaching the Final, all execution in the Activity diagram is aborted.


Activity Diagram Connector Toolbox Icons



See also

Control Flow connector

The Control Flow connects two nodes in an Activity diagram, modeling an active transition.

Control Flow
Object Flow connector

An Object Flow connects two elements, with specific data passing through it, modeling an active transition.

Object Flow
Interrupt Flow connector

The Interrupt Flow defines the two UML concepts of connectors for Exception Handler and Interruptible Activity Region.

Interrupt Flow


  • You can create Analysis diagrams (Simplified Activity diagrams) containing the elements most useful for business process modeling, using the 'New Diagram' dialog
  • You can perform model simulations on Activity models, and the model that you simulate can contain elements from more than one Package; to include the external elements in the simulation, you must create a Package diagram containing the 'parent' Package and the 'external' Packages containing the external elements, then create a Package Import connector from the parent Package to each external Package

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