UML Activity Diagrams

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UML Activity Diagrams-OOAD Lecture notes
Activity Diagram 
  • The main reason to use activity diagrams is to model the workflow behind the system being designed
  • Activity diagrams are also useful for analyzing a use case by describing what actions need to take place and when they should occur 
  • An activity diagram shows the flow from activity to activity 
  • An activity is an ongoing non-atomic execution within a state machine
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Activity diagram contains 
  • Activity states and action states 
  • Transitions 
  • Objects 
Action States 
  • The executable, atomic computations are called action states because; they are states of the system, each representing the execution of an action 
  • They cannot be decomposed and atomic, meaning that events may occur, but the work of the action state is not interrupted 
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Activity States 
  • Activity states can be further decomposed 
  • Activity states are not atomic, i.e., they may be interrupted
  • They take some duration to complete 
  • Activity states are also special kinds of states in a state machine
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Transitions
  • Transitions show the path from one action or activity state to the next action or activity state 
  • A transition is represented as a simple directed line 
  • Triggerless control passes immediately once the work of the source state is done 
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Branching 
  • It represents a branch as a diamond 
  • A branch, represented as a diamond, may have one incoming transition and two oi more outgoing ones
  • Each outgoing transition contains a guard expression, which is evaluated only once on entering the branch
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