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Advanced States and Transitions in UML State Machines

Advanced States and Transitions in UML State Machines-OOAD Lecture Notes
Advanced States and Transitions
  • Entry and Exit Actions 
  • Internal Transitions
  • Do-Activities
  • Deferred Event
Entry and Exit Actions: 
  • Entry actions are actions done upon entry of a state and are shown by the keyword event 'entry' with an appropriate action 
  • Exit actions are actions done upon exit from a state marked by the keyword event 'exit', together with an appropriate action
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Internal Transitions: 
  • Internal transitions are events handled internally without leaving the state 
  • Internal transitions may have events with parameters and guard conditions
Do-Activities: 
  • Activities that make use of object's idle time when inside a state
  • 'do' transition specifies the work done inside a state after the entry action is dispatched
Deferred Event: 
  • A deferred event is a list of events whose occurrence in the state is postponed until a state in which the listed events are not deferred 
  • It becomes active at the time they occur and may trigger transitions as if they had just occurred 
  • A deferred event is specified by listing the event with the special action 'defer'
SUB STATES
  • Sequential Substates
  • History States
  • Concurrent Substates
Sequential Substates
  • Sequential substates are those substates in which an event common to the composite states can easily be exercised by each state inside it at any time 
  • Sequential substates partition the state space of the composite state into disjoint states 
  • A nested sequential state machine may have at most one initial state and one final state
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History States 
  • It allows composite state that contains sequential substates to remember the last substate that was active in it prior to the transition from the composite state 
  • A shallow history state is represented as a small circle containing the symbol 'H' 
  • The first time entry to a composite state doesn't have any history 
  • The symbol 'H' designates a shallow history, which remembers only the history of the immediate nested state machine 
  • The symbol 'H*' designates deep history, which remembers down to the innermost nested state at any depth 
  • If there is only one level of nesting, shallow and deep history states are semantically equivalent
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Concurrent Substates 
  • Concurrent substates specify two or more state machines that execute in parallel, in the context of the enclosing object 
  • Execution of these concurrent substates continues in parallel 
  • These substates wait for each other to finish to join back into one flow 
  • A nested concurrent state machine does not have an initial, final, or history state
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