Chapter1220.docx

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Chapter1220

Chapter12

Object-OrientedAnalysisPhase

Theexercisesinthischaptergivestudentstheirfirstpracticalexposuretotheobject-orientedparadigm.Itisimportanttostressthatrepeatediterationisanintrinsicqualityofthisparadigm,andofobject-orientedanalysis（OOA）inparticular.Forexample,problems12.2and12.4seemextremelystraightforward.However,thestudentswillhavetoiterateanumberoftimesbetweenuse-casemodeling,classmodeling,anddynamicmodelingbeforetheyarriveatanacceptablesolution.（Ingeneral,theremaybemorethanoneacceptablesolutiontoagivenproblem.）

problemsolutions

12.1:

ThestatediagramsforclassesButton,Elevator,andElevatorDoorsareshowninFigures12.1,12.2,12.3,and12.4,respectively.

Figure12.1.StatediagramforclassButton.

Figure12.2.StatediagramforclassElevator.

Figure12.3.StatediagramforclassElevatorDoors.

Figure12.4.Use-casediagramforlibrarycirculationsystem.

12.2:

Use-CaseModeling

SeeFigure12.4.Figure12.5showstheexpandedscenarioforcheckingoutabook;theexpandedscenariosforreturningabook,removingabook,addingabook,requestingabooktobeheld,ormakingaqueryaresimilar.

Borrowerhandsbooktobecheckedouttolibrarian.Borrowerpreviouslyhadholdplacedonbook.

1.LibrarianentersCatcomputerterminal,thenscansbookandborrower’scardwithbarcodereader.

2.Book’sborrowernumberisupdated.

3.Holdinformationiscleared

PossibleAlternatives

A.Bookhadnotpreviouslybeenonhold.

Figure12.5.Expandedscenarioforcheckingoutabook.

ClassModeling

Candidateclassesaredeterminedusingnounextraction.

Stage1.ConciseProblemDefinition:

Anautomatedlibrarycirculationsystemistobeconstructed.

Stage2.InformalStrategy:

Anautomatedlibrarycirculationsystemistobeconstructed.Eachbookinthelibrary,aswellaseachborrower,canbeidentifiedbyabar-code.Abookcanbecheckedoutprovideditisnotbeingheldforanotherborrower;atmostoneborrowercanplaceaholdonabookcheckedoutbyanotherborrower.Whenabookisreturned,itischeckedinbyalibrarian.Borrowersandlibrariansarepermittedtoqueryacatalogoflibraryholdings.Librariansmayalsomodifythecatalog.

Stage3.FormalizetheStrategy:

Anautomatedlibrarycirculationsystemistobeconstructed.Eachbookinthelibrary,aswellaseachborrower,canbeidentifiedbyabar-code.Abookcanbecheckedoutprovideditisnotbeingheldforanotherborrower;atmostoneborrowercanplaceaholdonabookcheckedoutbyanotherborrower.Whenabookisreturned,itischeckedinbyalibrarian.Borrowersandlibrariansarepermittedtoqueryacatalogoflibraryholdings.Librariansmayalsomodifythecatalog.

Withregardtothenounsinthepreviousparagraph,borrower,librarian,andbar-codedonotchangewhilethelibraryisoperating;inobject-orientedterminology,theydonothaveaninternalstate.Accordingly,thesenounscannotcorrespondtoclasses.Inaddition,library,hold,holding,andsystemareabstractnouns.Finally,catalogisinformationthatrelatestobooks.ThisleavesBookasthesolecandidateclass.

TheclassdiagramisshowninFigure12.6.

Book

booknumber:

integer

author:

char[41]

title:

char[41]

subject:

char[41]

borrowernumber:

integer

holdnumber:

integer

Figure12.6.Classdiagramforlibrarycirculationsystem.

Figure12.7.Statediagramforlibrarycirculationsystem.

DynamicModeling

Figure12.7showsthestatediagramforclassBook.Itreflectsthevariousstatesthroughwhichabookmaymove,andthetransitionsbetweenthosestates.

Figure12.8.Use-casediagramforATMproduct.

12.3:

AsexplainedinSection11.6ofObject-OrientedandClassicalSoftwareEngineering,FifthEdition,anFSMisaquintuple.Innonmathematicalterms,anFSMconsistsofstatesandtheinputsthatresultinatransitionfromstatetostate.Forobject-orientedmodeling,however,wealsowanttoincorporatetheactionthatistobetakenonenteringastate.

Furthermore,thisshouldappearaspartofthestatediagram.Thissimplifieslaterdevelopment,particularlytheobject-orienteddesignphase.However,theresultingformalismwillnotbeformal,apricewearewillingtopaybecauseOOAasawholeisasemiformaltechnique.

12.4:

Use-CaseModeling

Theuse-caseisshowninFigure12.8.Figure12.9isanexpandedscenarioforwithdrawingfunds;theexpandedscenariosfordeposit,transfer,andbalancerequestaresimilar.

1.UserinsertscardintoATMandthenentersPIN.

2.ATMverifiesthatPINiscorrect.

3.Menuappearsonscreen.

4.Userchoosestowithdrawfunds.

5.Userenters$60asamounttobewithdrawn.

6.Adequatefundsareavailable,somachineupdatesuser’saccountbalance.

ATMdispensesmoney.

7.ATMprintsreceiptshowingnewbalance.

PossibleAlternatives

A.UserentersincorrectPIN.

B.Userrequests$50.

C.Userhaslessthan$60inaccount.

Figure12.9.Expandedscenarioforwithdrawingfunds.

ClassModeling

Thecandidateclassesarechosenusingnounextraction.

Stage1.ConciseProblemDefinition:

Asystemtocontrolanautomatictellermachine（ATM）istobeconstructed.

Stage2.InformalStrategy:

AsystemtocontrolanATMistobeconstructed.Afteracustomer’scardhasbeensuccessfullyverified,thecustomermaydepositandwithdrawmoneyfromanaccount,inquireaboutthebalanceofanaccount,andtransferfundsbetweentwoseparateaccounts.

Stage3.FormalizetheStrategy:

AsystemtocontrolanATMistobeconstructed.Afteracustomer’scardhasbeensuccessfullyverified,thecustomermaydepositandwithdrawmoneyfromanaccount,inquireaboutthebalanceofanaccount,andtransferfundsbetweentwoseparateaccounts.

Withregardtothenounsinthepreviousparagraph,ATM,card,andcustomerdonotchangewhilethesystemisoperating;inobject-orientedterminology,theydonothaveaninternalstate.Also,fundsandmoneyareabstractnouns.Finally,balanceisapropertyofaccount.Thus,thesolecandidateclassisAccount.

TheclassdiagramisshowninFigure12.10.

Account

accountnumber:

integer

balance:

float

PINnumber:

integer

Figure12.10.ClassdiagramforATMproduct.

DynamicModeling

Figure12.11showsastatediagramfortheATMasawholebecauseclassAccountdoesnotmovefromstatetostate.

Figure12.11.StatediagramforATMproduct.

12.5:

Object-orientedanalysisconsistsofthreesteps:

use-casemodeling,classmodeling,anddynamicmodeling.Itispossible,intheory,todothedynamicmodelingstepbeforetheclassmodelingstep.However,thisisnotadvisable,becausewhentheclassesareeventuallyextracted,majorchangesinthestatediagramarealmostcertaintoberequired.Thereasonisthatthestatediagram（essentiallyafinitestatemachine）cannotrepresentoridentifyinheritance.Thus,thelatestpointatwhichclassescanbeintroducedisthestartoftheclassmodeling

12.6:

Itispossible（thoughnotadvisable）tousetherapidprototypeasawayofdeterminingwhattheclassesshouldbe.Thus,classeswouldbeintroducedearlyintherequirementsphase.

Alternatively,classmodelingcouldprecedeuse-casemodelingintheobject-orientedanalysisphase,andclasseswouldbeintroducedattheverybeginningoftheobject-orientedanalysisphase.However,thisapproachwouldprecludeexperienceddevelopersfromextractingtheclassesfromthescenariosorusingCRCcards.

12.7:

Awidevarietyofformalismscouldbeused,bothgraphicalandtextual.Allthatisrequiredisthattheformalismshouldreflectthevariousstates,transitions,andactionsthatareinvolved.

However,suchformalismsarelessconvenienttouse.Forexample,themathematicalformalismofSection11.6ofObject-OrientedandClassicalSoftwareEngineeringislesssuitablethantheoneusedhere.Textualformalismsareequallyunsuitable.

12.8:

Theprincipleofstepwiserefinementrequiresasmanydecisionsaspossibletobepostponed.Alltheoperationsthathavetobeincludedintheproduct（“methods”）musteventuallyappearinthestatediagram.However,assigningthemethodstospecificclassescanwaituntilthedesignphase.Ontheotherhand,modelingbecomesextremelycomplexunlesstheattributesareassignedtotheirspecificclasses.

Infact,thereisanothergoodreasontowaituntilthedesignphasebeforeallocatingmethodstoclasses,namelythatthechoiceofarchitecture（forexample,client-server）willaffectwheretheclassesarephysicallylocated,andhencemayaffecthowtheoperationsareorganizedintomethods,andwhichmethodsshouldbeallocatedtowhichclasses.

termproject

12.9:

Use-CaseModeling

Theuse-caseforupdatingapatientisshowninFigure12.12;acorrespondingexpandedscenarioisshowninFigure12.13.

Figure12.12.Use-casediagramforupdatingapatientrecord.

1.ThenursequeriesthepatientnumberfromtheCPEdatabase

2.Thenurseviewsthepatientrecord.

3.IfthenursenoticesthatthepatientneedsJCFassistancethenurseupdatesthepatientrecordtoreflecttheJCFneed.

4.IfthenursenoticesthatthepatientneedsWFassistancethenurseupdatesthepatientrecordtoreflecttheWFneed.

5.IfthenursenoticesthatthepatientneedsJCassistancethenurseupdatesthepatientrecordtoreflecttheJCneed.

6.Whenthepatientisdischarged,thenurseentersthedischargedate.

7.ThenurseinsertstheupdatedrecordintotheCPEdatabase

PossibleAlternatives

A.Thepatientnumberdoesnotrepresentacurrentlyregisteredpatient.

B.Thenursenoticesthatthepatientdoesnotlivewithin500milesofBACH;suchapatientisnoteli