Statechart Diagrams

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Statechart Diagrams

• Keng Siau
• University of Nebraska-Lincoln

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Statechart Diagrams

• A statechart diagram shows a state machine
• One of the diagrams in the UML for modeling the
  dynamic aspects of systems
• For the most part, this involves modeling the
  behavior of reactive objects
• A reactive object is one whose behavior is best
  characterized by its response to events
  dispatched from outside its context

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Activity and Statechart Diagrams

• An activity diagram is a special case of a
  statechart diagram in which all or most of the
  states are activity states and all or most of the
  transitions are triggered by completion of
  activities in the source state

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Activity and Statechart Diagrams

• An activity diagram shows flow of control from
  activity to activity
• A statechart diagram shows flow of control from
  state to state
• Statechart diagrams may be attached to classes,
  use cases, or entire systems in order to
  visualize, specify, construct, and document the
  dynamics of an individual object

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Terms and Concepts

• A statechart diagram shows a state machine,
  emphasizing the flow of control from state to
  state
• A state machine is a behavior that specifies the
  sequences of states an object goes through during
  its lifetime in response to events, together with
  its responses to those events

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Terms and Concepts

• The state of an object is a condition or
  situation during the life of an object during
  which it satisfies some condition, performs some
  activity, or waits for some event
• An event is the specification of a significant
  occurrence that has a location in time and space

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Terms and Concepts

• A transition is a relationship between two states
  indicating that an object in the first state will
  perform certain actions and enter the second
  state when a specified event occurs and specified
  conditions are satisfied

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Terms and Concepts

• An activity is an ongoing nonatomic execution
  within a state machine
• An action is an executable atomic computations
  that result in a change in state of the model or
  a return of a value

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Statechart Diagrams

• Graphically, a statechart diagram is a collection
  of vertices and arcs
• Statechart diagrams commonly contain
• Simple states and composite states
• Transitions, including events and actions

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Statechart Notation
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Statechart Diagram
Add student count lt 10
Add Student /
Set count 0
Initialization
Open
do Initialize course
entry Register student
exit Increment count
Cancel
Cancel
count 10
Canceled
Closed
do Notify registered students
Cancel
do Finalize course
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Statechart Diagram
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Statechart Diagram
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Statechart Diagram
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Statechart Diagram
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Statechart Diagram
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Statechart Diagram
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Statechart Diagram
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Modeling Reactive Objects

• The most common purpose of statechart diagrams is
  to model the behavior of reactive objects
• Specify three things
• The stable states in which that object may live
• The events that trigger a transition from state
  to state
• The actions that occur on each state change