Activity Diagrams

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Activity Diagrams

• Derived from several techniques
• Event diagrams of Jim Odell
• SDL state modeling techniques
• Workflow modeling
• Petri nets
• Especially useful when
• Modeling a workflow
• Modeling an operation
• Describing behavior that has a lot of parallel
  processing

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Activity

• Activity is the state of doing something
• Real-world process like typing a letter
• Execution of a software routine like a method on
  a class.
• Rounded rectangle is narrower and more
  oval-shaped than the state icon.

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Activity Diagrams vs. State Diagrams

• Activity diagram describes the sequencing of
  activities, with support for both conditional and
  parallel behavior
• Activity diagram is a variant of a state diagram
  in which most, if not all, the states are
  activity states.
• Much of the terminology used in Activity diagrams
  follows that of state diagrams.

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Activity Diagram
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Activity vs.State Diagrams
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Activity vs. State Diagrams
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Activity Diagram
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Activity Diagrams

• Activity diagrams
• allow the user to choose the order in which to
  do things
• states the essential sequencing rules that must
  be followed
• Flowcharts are limited to sequential processes,
  whereas activity diagrams can handle parallel
  processes

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Forks Joins

• A join synchronizes parallel behavior
• Forks and joins must match every time you have
  a fork, you must have a join that combines the
  threads started by that fork.

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Forks Joins

• Extensions to previous rule
• A thread that comes out of a fork can itself
  fork, with the new threads coming back together
  before reaching the matching join

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Forks Joins

• Extensions to previous rule
• If a thread coming out of a fork goes straight
  to another fork, you can remove the second fork
  and just have the threads from the second fork
  coming out of the first fork.

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Decomposing an Activity

• An activity can be broken down into subactivities
  using notation similar to superstates and
  substates on a state diagram.

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Activity Diagram
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Dynamic Concurrency
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Swimlanes

• Our activity diagrams so far have focused on what
  happens, but they do not tell you who does what.
• Communication among responsible objects is
  missing.
• Swimlanes can be used to arrange activity
  diagrams into zones of responsibility.

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Activity Diagram
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Assigning Objects to Activities

• The task of assigning objects to activities
  should be done.
• Should it be done immediately when initially
  diagramming activities, or later when an overall
  sense of the behavior is understood?

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Activity Diagrams

• Strengths
• Support and encourage parallel behavior
• Good tool for workflow modeling
• Good tool for multithreading
• Weaknesses
• Links among actions and objects are not
  especially clear
• Interaction diagrams are more helpful in this area

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When to use Activity Diagrams

• Analyzing a Use Case
• Understanding Workflow
• Describing a complicated sequential algorithm
• Dealing with multithreaded applications

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When not to use Activity Diagrams

• Trying to see how objects collaborate
• Trying to see how an object behaves over its
  lifetime
• Representing complex conditional logic

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ObjectFlow
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ESU Revisited

• Preparing for Registration
• The process of preparing the course curriculum
  and making it available to the student community
  can be expressed using an Activity Diagram.
• We dont assign responsibilities to each activity
  at this time.

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ESU Revisited
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ESU Revisited

• Preparing for Registration
• We must make sure all courses have been assigned
  a professor

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ESU Revisited
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The UML and Design Flow
Collaboration Diagram
Use Case
Sequence Diagram
State Diagram
Class Diagram Activity Diagram
Object Diagram