CH 5:: STATE MODELING. Prepared by: Ms. Pankti Dharwa (SVBIT)

Transcription

1 CH 5:: STATE MODELING Prepared by: Ms. Pankti Dharwa (SVBIT)

2 EVENTS An event is something which happens outside the thing which is being considered, possibly requiring some action to be taken. i.e.an occurrence at a point in time. Events may be caused by the arrival of some data, or some simple stimulus which may be due to human activity or some other part of the system. For example, Keystroke is an event for the keyboard, power turn on,alarm set,etc.

3 TYPES: Signal. Change & Time event Signal: Flight 121 departs from Chicago on Jan 21, 2012 Change: When(temp < heating set point) When( power< lower limit) Time: When(date=21,feb,2012) After(10 seconds)

4 STATE Abstractions of values & links of object. set of values & links are grouped together into state according to behavior of object. Ex:- State of phone waiting/dialing Freezing point Waiting Dialing Powered Object finite no. of possible state but one time object can be in one state

5 Object respond to certain event when it is in certain state. Event represents points in time Power turned on Power turned off Power turned on Powered Not Powered state represents intervals of time. STATE :- a condition or situation during the life of an object at which time it satisfies some condition, performs some activity, or waits for some event.

6 TRANSITIONS & CONDITIONS Transition is change from one state to another. Ex:- called phone is answered, phone line transitions from RINGING state to CONNECTED state. GUARD CONDITION :-It s a Boolean expression that must be true in order for transition to occur Ex:- When you go out in morning (event) if temp. is below freezing (condition) then put on your gloves (next state) Guard condt. checked only once, at time the event occurs & transition fires if cond. is true

7 STATE DIAGRAM graph whose nodes = state & Arcs = transitions between states specifying the sequence of states it goes through during its lifetime in response to events, together with the responses to those events describe changes in state in a procedure.

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9 ONE SHOT DIAGRAM Represents objects with finite lives & have initial & final states. Initial State creation of object final state destruction of object. White's Turn checkmate Black moves white moves statemate statemate Black's Turn checkmate LIFE CYCLE OF CHESS GAME WITH INITIAL & FINAL STATE

10 Using entry, exit point

11 STATE DIAGRAM BEHAVIOUR:: ACTIVITY EFFECTS Specifies an optional behavior to be performed when the transition fires. Effect is reference to behavior that is executed in response to event. Ex:- disconnect phone line activity is executed in response to onhook event A program increment an internal counter every time particular event occurs.

12 Notation :- / & name of activity following event that causes it right button down / display pop-up menu Idle right button up / erase pop up menu Menu Visible cursor moved / highlight menu item Activities for pop-up menu:- Activity is behavior that can be executed in response to event

13 ::DO ACTIVITIES Activity that continues for an extended time. Occur within state only & can not be attached to transition Ex:- warning light may flash during paper jam state for copy machine Paper Jam do / flash warning light Notation :- do / name of activity

14 ::ENTRY & EXIT ACTIVITIES Bind activities to entry or to exit from a state An entry activity is a behavior that occurs while the object is transitioning into the state An exit activity occurs as part of the transition out of the state.

15 Ex:- control of garage door opener user generates depress event with pushbutton to open & close door the control generates motor up & motor down activities depress / motor up Opening door open / motor off Closed depress / motor up Open door closed / motor off depress / motor down Closing

16 whenever state is entered by any incoming transition the entry activity is performed whenever state is exited by any outgoing transition the exit activity is performed NOTATION :- entry activity - keyword entry & / char Exit activity - keyword exit & / char depress Opening entry/motor up door open Closed entry/motor off door closed depress Closing entry/motor down depress Open entry/motor off

17 ::COMPLETION TRANSITION: An arrow without event name indicates automatic transition that fires when activity associated with state is completed such a unlabeled transition is called completion transition. Race condition: object can receive signal from more than one object, the order in which concurrent signals are received may effect final state. Basic state diagram notations Diagram name State1 Do/activity Event/effect event(attri.)[condition]\effect State2 Do/activity Event/effect

18 Idle offhook onhook / disconnectline Timeout Dial Tone do / SoundDialTone timeout do / soundloudbeep digit(n) digit(n) timeout Warning do / playmessage Dialing invalidnumber BusyTone do / slowbusytone numberbusy validnumber RecordedMessage do / playmessage onhook / disconnectline Connecting FastBusyTone trunkbusy do / findconnection routed do / fastbusytone Ringing do / ringbell calledphoneanswers / connectline Connected messagedone CalledPhoneHangsUp / disconnectline Disconnected

19 State Transition Diagram for a Digital Watch

20 Prepare a state diagram of an extension ladder An extension ladder has a rope, pulley & latch for raising, lowering & locking the extension. When latch is locked the extension is mechanically supported & you may safely climb ladder. to release latch you raise the extension slightly with rope. You may then freely raise or lower the extension. The latch produces a clacking sound as it passes rung of ladder. The latch may be reengaged while raising the extension by reversing direction just as the latch is passing a rung.

21 Extension Ladder Latch is locked do/ climb up the ladder release the latch extension changed do/ freely raise / lower the extension Passing a rung of ladder Clacking Sound