1. Activity Diagrams

2. Introduction An activity diagram...
Models the dynamic aspects of a system.
Serves the same function as a flowchart.
Is composed of a sequence of activities, possibly concurrent.
An activity is an ongoing non-atomic execution within a state machine.
Each activity generates actions.
Actions are atomic computations that result in a change of state or the return of a value.
Is commonly used to show the activities involved in carrying out a particular use-case.

3. Terms and Concepts An activity diagram…
Shows the flow from activity to activity.
Is graphically rendered as a collection of vertices and arcs.
Commonly contains activity states, action states, transitions and objects.

4. Terms and Concepts

5. Terms and Concepts An action state…
Represents an atomic computation that takes an insignificant amount of time.
Cannot be decomposed.

6. Terms and Concepts An activity state…
Represents a computation that can be decomposed into other activities and actions.
Is not atomic.
Takes some duration to complete.
Is graphically rendered the same as an action, but may contain entry and exit actions.

7. Terms and Concepts A transition…
Shows the path between activity and action states.
Is graphically represented as a directed line.

8. Terms and Concepts Branching…
Is used to show alternate flows of control.
Is represented as a diamond. Outgoing transitions are labeled with Boolean expressions

9. Terms and Concepts Forking and Joining
A fork is when a single flow of control splits into two or more parallel (concurrent) flows of control.
A join is when two or more flows of control merge into a single flow of control.
A flow of control is also known as a thread.
A synchronization bar is used to model forking and joining, and is modeled as a thick horizontal or vertical bar.

10. Terms and Concepts

11. Terms and Concepts Swimlanes...
Are used to group activities according to the organization responsible for those activities.
Are eventually implemented by one or more classes.
Are divided by solid vertical lines.
Can be used in the context of concurrency.
An activity can only belong to one swimlane, but transitions between activities may cross swimlanes.

12. Terms and Concepts

13. Terms and Concepts Object Flow
Objects may be attached (using dependencies) to specific activities in an activity diagram.
The activity to which an object is connected has a direct effect on the object’s state or lifetime.
An object’s state may be shown in brackets inside the object rectangle.

14. Terms and Concepts

15. Common Modeling Techniques
Use activity diagrams in the same situations you would use flowcharts - to model operations and work flows.
Feel free to insert actors and objects into your activity diagrams to show which activities they are directly involved with.
You can attach activity diagrams to classes, interfaces, components, nodes, use cases and collaborations