StudentAnswersChapter05Word文档下载推荐.docx

StudentAnswersChapter05Word文档下载推荐.docx

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Asitisresponsibleformaintainingdata,itmightbearguedthattheentitystereotypewasappropriate.Thisstereotypeisnormallyusedfordatainthesystemthatrepresentsasingleexternalentity,however.Therestaurantobjectdoesnotrepresentanentityinthissense,however,butinsteadmakesotherentitiesavailableinthesystem.Theentitystereotypeisprobablynotappropriatefortherestaurantobject,therefore.

Thereisacontrolaspecttotherestaurantobject,asitiscontrollingaccesstotheentitydataheldbythesystem.Thisismoreaquestionofbeinga`gatekeeper'

tosomesystemresourcesthancontrollinganumberofinteractions,asthebookingsystemobjectdoes,anditisprobablyclearernottorepresentbothbythesamestereotype.

Itthereforeappearsthatnoneoftheanalysisclassstereotypesstraightforwardlyappliestotherestaurantobject,andithasbeenleftinFigure5.4asaplainobject.

SuggestedanswerforExercise5.2

Thedateattributeinthebookingsystemclassrepresentsthedateforwhichbookinginformationiscurrentlybeingdisplayedbythesystem.Thedateattributeinthe`current'

bookingsshouldbethesameasthis,therefore,otherwisethesystemwillbedisplayingbookingsforthewrongdate.Thiscanbespecifiedbyaconstraintonthe`current'

associationasshownbelow.

SuggestedanswerforExercise5.3

Onthefaceofit,thisproposalmightseemtobeattractiveonthegroundsofremovingredundancy,followingtheguidelinethatdatashouldnotbestoredinmorethanoneplace.However,removingthedateattributefromthebookingsystemobjectwouldcreateproblemsinthesituationwheretherearenobookingsyetrecordedforadatethesystemisaskedtodisplay.Inthiscase,thesystemwouldhavenorecordofwhatdatewascurrentlybeingdisplayed.Ifawalk-inbookingwasthencreated,forexample,itwouldbedifficulttoworkoutthedaterequiredforthenewbookingobject.

Thissuggeststhatstoringthedateinbothclassesisnotinfactredundant,asthetwooccurrencesoftheattributehavedifferentsemantics,onereferringtothedatebeingdisplayedbythesystem,andtheothertothedateofanindividualbooking.Incaseslikethis,careneedstobetakenbefore`optimizing'

oneoftheattributesaway.

SuggestedanswerforExercise5.4

Producingarealizationforthisscenarioinvolvesdecidingwhichobjectisresponsiblefordetectingthatthedateisinvalid.Areasonableguidelinetoadopthereistovalidateuser-entereddataassoonaspossible.Thiswouldmeanthatthebookingsystemobjectshouldberesponsiblefordetectingerrors,andsoarealizationmightbeasfollows.

Therestaurantandbookingobjectshavebeenleftonthisdiagramtoemphasizethattheydonotreceiveanymessagesinthecourseofthisinteraction.Itisnotnecessaryatthislevelofdetailtoattempttospecifyhowthesystemreportstheerrortotheuserandrequestsreentryofthedate.Wecansimplyassumethatwhentheuserreentersthedateanewsystemmessagewillbegenerated,andeithertheinteractionaboveortheoneinFigure5.5willtakeplaceagain.

SuggestedanswerforExercise5.5

Thecompletesequencediagramisshownbelow.

SuggestedanswerforExercise5.6

Thesequencediagramfor`Recordwalk-in'

isshownbelow.Apartfromchangingtheactor,classandoperationnamesthroughouttorefertowalk-ins,themostsignificantchangeisthatacustomerobjectdoesnotneedtobelocated.Detailsreferringtocustomershavethereforebeenremovedfromthediagram.

SuggestedanswerforExercise5.7

Arealizationforthecasewherethecustomerisalreadyknowntothesystemisshowninthediagrambelow.AsinFigure5.5,therestaurantobjectretrievesdatafromcustomerobjectstocomparewiththenameandphonenumberoftherequestedcustomer.Assumingthatamatchisfound,acustomerobjectisreturnedtothecaller.

Inthecasewherenomatchingcustomerisfound,anewinstanceiscreatedandareferencetoitisreturnedtothecaller,asshownbelow.

SuggestedanswerforExercise5.8

Apossiblesequencediagramfortabletransferisshownbelow.Therequiredtableisfirstselected,asshowninFigures5.9and5.11.Thenthetableobjectcorrespondingtothenumberofthenewtableisretrievedfromtherestaurantobject,asinFigure5.8.Finally,thetableallocatedtotheselectedbookingisupdated,andthedisplayrefreshed.

Analternativedesignmightpassthetablenumbertotheselectedbooking,whichwouldthenhavetoretrievetherequiredtableobjectfromtherestaurantitself.Thisdesignisslightlymore`decentralized'

thantheoneabove,butontheotherhandintroducesacirculardependencybetweenthebookingandrestaurantclasses.Thedesignshownaboveisthereforeprobablypreferable.

SuggestedanswerforExercise5.9

ThediagramsbelowshowtheclassesfromFigure5.13withtypeinformationaddedtoattributesandoperations.TheadditionsarestrictlybasedonwhatisstatedinthevariousrealizationsgiveninChapter5,anddonotattempttodefinefinalsignaturesfortheoperations.Thiswillbeconsideredlaterwhenimplementingeachclass.

Wheredetailedparametershavenotyetbeendefined,typessuchasBookingIdandBookingDetailshavebeenusedasplaceholders.TheOCLcollectiontypeSet（T）hasbeenusedtoindicatethattheRestaurant.getBookingsoperationreturnsingeneralmorethanonebookingsobject.