State Modeling New

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State Modeling


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Introduction

The structure of objects and their relationships to eachother in a system described by its static structure i.e.the class model.

Some objects in a system have complex temporalbehaviors, which must be carefully design.

Temporal phenomena that occur over an interval oftime are properly modeled with a state

The state model examine changes to the objects andtheir relationships over time

The state model describes the sequence of operationsthat occur in response to events external stimuli!


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Events occurrence at a point in time

instantaneous often corresponds to verb in past tense

e.g., alarm set, powered on

or onset of a condition e.g., paper tray becomes empty, temperature drops below

free"ing

may logically precede or follow another ormay be unrelated e.g., #light $%& must depart ''( before it can arrive in 'elhi

causally related! e.g., #light $%& may depart before or after )ight &*+ departs

''( causally unrelated!

Concurrent event: causally unrelated

eventshave no e-ect on one another


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inds of events

Signal event/ the event of sending or receiving of a signal Signal/ an explicit one0way transmission of

information from one object to another may be parameteri"ed

1.g., stringEntered(Foo) sending of a signal by one object is a

distinct event from its reception by another 'i-erence between signal and signal event

every signal transmission is a uniqueoccurrence but we group them into signalclasses to indicate common structure andbehavior. 1.g., I2 )ight $%& departs from ''( on 3an $$, %4$& is

an instance of #light'eparture


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Signal class 0 5M6 notation

77 signal 88

FlightDeparture

airline)ight(umcity

date

9eyword :signal; in 77 88

name of signal class

attributes


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inds of 1vents

Change event 1vent caused by satisfaction of a


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inds of 1vents

Time event 1vent caused by the occurrence of an absolute

time or the elapse of a time interval

for absolute time the 5M6 (otation/ 9eyword

when followed by parenthesi"ed expressioninvolving time

whendate = 3an $, %4$&!

for time interval the 5M6 (otation/ 9eyword

after followed by parenthesi"ed expressionthat evaluate to a time duration

aftern time5nits!

after$4 seconds!


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States an abstraction of values and lin9s of an object

behavioral condition that persists in time according to gross behavior of objects, set of

values and lin9s are grouped together into astate

often corresponds to verbs with su>x of :0ing;

e.g.,


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Aontd. In deBning states

ignore attributes that do not a-ect the behavior of the object lump together in a single state all combinations of values and lin9s

with the same response to events

1.g., except for leading 4Cs D $Cs, the exact digits dialed do not a-ectthe control of the phone line, so we can deBne a state Dialingandtrac9 the phone number as a parameter

Ebjects in a class have a Bnite number of possible states 1ach object can only be in one state at a time

2t a given moment of time, the various objects for a class can existin a multitude of states

2 state speciBes the response of an object to input events 1.g., if a digit is dialed in state DialTone, the phone line drops the

dial tone and enters state Dialing;

If the receiver is replaced in state DialTone, the phone line goesdead and enters state Idle.


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Symmetry between 1vents and

States

1vents represent points in time

State represent intervals of time. 2state corresponds to the intervalbetween two events received by anobject

@ower turnedon

@ower turnedo-

@ower turnedon

@owered (ot @owered


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Transitions and Aonditions

ransition/ an instantaneous change in state triggered by an event

Transition is said to Bre upon the change from source totarget state

Erigin and target state of a transition are di-erent states

but may be the same e.g., when a phone line is answered, the phone line

transitions from the Ringingstate to the Connectedstate.

!uard Condition/ boolean expression that must be true for transition to occur

chec9ed only once, at the time event occurs transition Bresif true

1.g., when you go out in the morning (event), if thetemperature is below free"ing (condition), then put onyour gloves (next state).


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1nabling and Bring of transitions

Transition is/ enabled when source state is active and guard

condition satisfed

freswhen enabled and the triggering eventoccurs

1xample below/ enabled when current state is 1diting and the

form is complete Bres when the user presses the :E; button

Editing Submitted

pressOK[form complete]


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State 'iagrams

a graph whose nodes are states and whosedirected arcs are transitions between states

speciBes state sequences caused by eventsequences

all objects in a class execute the state diagramfor that class diagram models their commonbehavior

(ote/ state names are unique within the scope ofstate diagram

2 class with more than one state has importanttemporal behavior

2 class is temporarily important if it has a single state

with multiple responses to events


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State diagrams

Fraphical state0modeling notation/ States/ labeled rounded boxTransitions/ directed arcs, labeled by triggering

event, optional guard condition, andGor e-ects

SpeciBes the response of an object to input

events0 ignores events except those for which behavior isprescribed

1xample/

S T

States


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State diagrams

S T

States

Transition

Fraphical state0modeling notation/ States/ labeled rounded boxTransitions/ directed arcs, labeled by triggering

event, optional guard condition, andGor e-ects

SpeciBes the response of an object to inputevents

0 ignores events except those for which behavioris prescribed

1xample/


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State diagrams

Fraphical state0modeling notation/ States/ labeled rounded box

Transitions/ directed arcs, labeled by triggeringevent, optional guard condition, andGor e-ects

1xample/

S T

event(attribs)[condition] / effect

States

1ventTransition


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State diagrams can represent Aontinuous loops

'o not care, how the loop is started

Ene0shot life cycles


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@hone 6ine example


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:Ene0shot; state diagrams

represent objects with Bnite lives have initial and Bnite states

initial state0 entered on objectcreation

Bnal state 0 entry implies destructionof object


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1xample

Whites

turn

Blacks

turn

white

moves

black

moves

checkmate

checkmate

stalemate

stalemate

Chess game

start state

Deault fnal state


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1xample

Whites

turn

Blacks

turn

Black

wins

White

wins

Drawwhite

moves

black

moves

checkmate

checkmate

stalemate

stalemate

Chess game

start state

Final

states


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1xample 0 entry and exitpoints

Whites

turn

Blacks

turn

white

moves

black

moves

checkmate

checkmate

stalemate

stalemate

Chess game

Black

wins

Draw

White

wins


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State Model

multiple state diagrams, one for eachclass with important temporalbehavior diagrams interact by passing events and

through side e-ects of guard conditions

events and guard conditions must

match across diagrams in the model


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'etails

if more than one transition leaves astate, then the Brst event to occurcauses the corresponding transition to

Bre if an event occurs and no transition

matches it, the event is ignored

if more than one transition matches anevent, only one transition will Bre butthe choice is non0deterministic


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2ctivity 1-ects

eect= reference to a behaviorexecuted in response to an event can be attached to a transition or a

state listed after a slash :G;!

multiple e-ects separated with a :,; and

are performed concurrently


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2ctivity 1-ects

Activity behavior that can beinvo9ed by any number of e-ects

May be performed upon/

a transition entry to or exit from a state

some event within a state

(otation/ eventG resulting0activity


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2ctivities

Eften useful to specify an activitythatis performed within a given state 1.g., while in Paper"amstate, the

warning light should be )ashing 1.g., on entry into the #peningstate,

the motor should be switched on

1.g., upon exit of the #peningstate,the motor should be switched o-


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2ctivity e-ects

Idle

Menu visible

r_button_down / showPopup

r_button_up / hidePopup


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'o02ctivities

PaperJam

do/ flash warning light

continue for an extended time

can occur only within a state

can not be attached to a transition

include

continuous operations, such as displaying a picture on atelevision screen

Sequential operations that terminate by themselves after an

interval of time

may be performed for all or part of time that an obect is in a state

may be interrupted by event received during execution! event

may or may not cause state transition


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1ntry and 1xit 2ctivities

Opening

entry / motor up

exit / motor off

can bind activities to entry to/ exit from a state

All transitions into a state perform the same activity, in

which case it is more concise to attach the activity to the state


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Erder of activities

1. activities on incoming transition

2. entry activities

3. doactivities!. exit activities

". activities on outgoing transition

#vents that cause transitions out of the state can interrupt

doactivities. $f a doactivity is interrupted, the exit

activity is still performed


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In general, any event can occurwithin a state and cause an activity

to be performed.

1ntry and exit are only two examples

of events that can occur

Diference between an event

within a state and sel-transition/ only the self0transitioncauses the entry and exit activities to

be executed but an event within a


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Aompletion Transition

triggered b com!letion o activit inthe so"rce state

Eften the sole purpose of a state is to

perform a sequential activity. ?hen the activity is completed, a

transition to another state Bres

2n arrow without an event name indicatesan automatic transition that Bres

State "

do / blah#$

State %


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Aontd.

If a state has one or more completion transitions,but none of the guard conditions are satisBed, thenthe state remains active and may become Hstuc9C.

The completion event does not occur a second time

Therefore no completion transition will Bre later tochange the state

So if a state has completion transition leaving it,normally guard condition should cover every

possible outcome. 'o not use guard condition on a completion

transition to model waiting for a change of value


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Sending signals 2 object can perform the activity of sending a signal to

another object. 2 system of objects interact by exchanging signals

The activity :send target!"(attributes); sends a signal S withthe given attributes to the target object.

1.g., the phone line sends a connect(phone number) signal to

the s#itcher #hen a complete phone number has beendialed!

2 signal can be directed to a set of objects or a single object.

If the target is a set of objects, each of them receives a

separate copy of the signal conc"rrentl and independentlyprocess the signal and determines whether to Bre a transitionor not

If an object receive signals from more than one object, theorder in which concurrent signals are received may a-ect the

Bnal state race condition!


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2dvanced state modeling

Aonventional state diagrams aresu>cient for describing simplesystems but need additional power

to handle large problems Model complex system by using

(ested state diagrams

(ested states Signal generali"ation

Aoncurrency


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(ested state diagram

@roblem with )at state diagram Aonsider an object with n independent


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(ested state

(est states to show their commonalityand share behavior

Com!osite state# state that enclosesthe nested states. 6abels in the outer contour

2 nested state receives the outgoing

transitions of its composite states


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1xample/ Transmission

ransmission

Forward

(eutraleverse

$st %nd &rd

downshift

upshift

downshift

upshiftstop

push (

push #

push (

push


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Signal Fenerali"ation

Ergani"e signals into generali"ation hierarchy

with inheritance of signal attributes Jiew every actual signal as a leaf on a

generali"ation tree of signals.

eceived signal triggers transitions that are

deBned for any ancestor signal type. 1.g., typing an HaC would trigger a transition on signal

2lphanumeric as well as signal eyboardAharacter.

2 signal hierarchy permits di-erent levels of

abstraction to be used in a model. 1.g., some state might handle all iGp characters the

same other states might treat control charactersdi-erently from printing characters .


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AE(A51(AK

State model supports concurrencyamong objects

Ebject can act D change stateindependent of one another.

Sometime objects shares constraintsthat causes their state changes

2FF1F2TIE(


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2FF1F2TIE(AE(A51(AK

State 2ggregation means collection ofstate diagrams , one for each part

:and; relationship

2ggregate state is one state from Brstdiagram D a state from second diagramD state from each other diagram.

Transition for one object depend onanother object that allows interactionbetween the state diagram.


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Aoncurrency within an


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Aoncurrency within anEbject

Some objects can be partitioned into subsetsof attributes or lin9s.

1ach of the partitioned subset has its ownsubdiagram.

The state of the object comprises one statefrom each subdiagram.

The sub diagrams need not be independent

the same event can cause transitions inmore than one subdiagram

5M6 (otation0 partition the composite stateinto regions with dotted lines.


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Synchroni"ation of Aoncurrent2ctivities

Sometimes one object must performtwo or more! activities concurrently.

The object must complete both

activities before it can progress to itsnext state.

or an o n


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or an o n#%

&plitting control and 'erging

control #E0 2 transition that for9s

indicates splitting of control into

concurrent parts.

3EI(0 1xplicit merging of concurrent

control by a transition.


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elation of class model, state model

2 state diagram describes all or part ofthe behavior of the objects of a givenclass.

States = classes of values D lin9 for anobject

State model of a class is inherited by its

subclasses. Subclass inherits both thestate D Transitions.

It is also possible to reBne an inherited

state diagram by expanding state into


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Aontd.

State structure is related to andconstrained by class structure. 2 composite state is the aggregation of

more than one concurrent substate.Try to ma9e the state diagrams of

subclasses independent of the statediagrams of their superclasses.

State Modeling New

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