Finite State Machines and StatechartsStatechart Graphical representation of finite state machineStates are rounded boxesTransitions are arcs Statechart relates events and states of a class of objectsEvent Causes change of state Referred to as state transition State A recognizable situation Exists over an interval of timeRepresents an interval between successive events

Events

EventA discrete signal that happens at a point in timeAlso known as a stimulus Has no durationTwo events May logically depend on each otherE.g, ATM Card inserted before Pin # enteredTwo eventsMay be independent of each otherE.g., ATM card read at Alexandria ATMATM Card read at Fairfax ATM

Events and Conditions

State transition label Event [Condition]Condition is a Boolean function Conditions are optional on statecharts Condition is true for finite period of timeWhen event occurs, condition must be true for state transition to occur.

Actions

State transition labelEvent / action(s)Event [condition] / action(s)Actions Executed as a result of state transitionExecutes instantaneously at state transition Terminates itself

Activities

ActivityExecutes for duration of stateEnable Activity on entry to stateDisable Activity on exit from stateExamples of activitiesIncrease SpeedExecutes for duration of Accelerating stateMaintain SpeedExecutes for duration of Cruising stateResume CruisingExecutes for duration of Resuming state