Activity Diagrams

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Activity Diagrams
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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.

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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.

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Terms and Concepts
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Terms and Concepts

• An action state
• Represents an atomic computation that takes an
  insignificant amount of time.
• Cannot be decomposed.

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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.

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Terms and Concepts

• A transition
• Shows the path between activity and action
  states.
• Is graphically represented as a directed line.

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Terms and Concepts

• Branching
• Is used to show alternate flows of control.
• Is represented as a diamond. Outgoing
  transitions are labeled with Boolean expressions

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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.

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Terms and Concepts
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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.

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Terms and Concepts
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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 objects state or
  lifetime.
• An objects state may be shown in brackets inside
  the object rectangle.

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Terms and Concepts
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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