Activity Diagrams

1
Activity Diagrams

• Describing Flows

2
Some terms

• Activity
• Something an object performs on an ongoing basis
• Non-atomic
• Can be interrupted
• Can be decomposed into sub-activities
• Actions
• Set of executable computations
• Results in
• Changes to values of one or more attributes or
• Return of a value to an object
• Cannot be interrupted
• UML symbol is the same for both activity and
  action ( a lozenge)

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Activity or action?

• Calculate shipping costs
• Update customer preferences
• shipCostcountryCodesubTotal
• Ship Order
• isDeliveredYes

4
Notation

• Diagrams are read from top to bottom
• Forks and branches
• branches and forks to describe conditions and
  parallel activities
• A fork is used when multiple activities are
  occurring at the same time
• A branch is a decision point

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Branching and Merging

• Branch is a decision point where there is more
  than one possible path for the activity
• Merge is a point where multiple branches come
  back together
• Represented by
• Both merge and branch use same notation

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Branching and Guard conditions

• Each path out of a branch has a guard condition
• Guard condition
• Boolean expression that evaluates to True or
  False
• Collection of all possible branches must cover
  all possibilities
• Sometimes, else is used to cover all bases
• Guard conditions cannot overlap (mutually
  exclusive)
• Guard condition shown in square brackets

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Example of branches and merges
8
Forks and Joins

• Fork
• Splitting of flow of control to two more flows of
  control
• Each flow is independent and concurrent
• Joins is the synchronization (or joining) of two
  or more flows into one
• Symbol for both is a synchronization bar

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Identify the forks, joins and synchronization bars
10
Swimlanes

• Activities and actions grouped by vertical lines
• Each pair of lines delineates the swimlane
  associated with a particular object.

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SWIMLANES
Accounting
Marketing
Shipping
Retrieve books from inventory
Update Customer Preferences
Post Ledger Item
Compute Subtotal
Look up country code
ship abroad
ship within US
shipCostcountrysubTotal
shipCostregionsubTotal
Compute new subtotal