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1、Chapter8: Object-RelationalModelingObject-OrientedSystemsAnalysisandDesignJoeyF.George,DineshBatra,JosephS.Valacich,JeffreyA.Hoffer8-1©PrenticeHall,2007ChapterObjectivesAfterstudyingthischapteryoushouldbeableto:Understandtherelationalmodel.Normalizedatatothethirdnormalform.Und
2、erstandtheobject-orientedextensionstotherelationalmodel.2©PrenticeHall,2007ChapterObjectives(Continued)Afterstudyingthischapteryoushouldbeableto:Realizetheroleofobjectrelationsinsystemsanalysis.Translateaconceptualdatamodelintoobjectrelations.Integrateobjectrelationsobtainedfr
3、omdifferentusecases.3©PrenticeHall,20074©PrenticeHall,2007Object-relationaldatamodelingconvertsaconceptualdatamodeltoalogicaldatamodelbasedonrelationalandobject-orientedtechnology.5©PrenticeHall,2007PurposesofObject-RelationalModelingProducedatabasestructuresCreateentityclasse
4、sEnhanceandfinalizetheattributesinthedatamodel6©PrenticeHall,2007WhatIsaRelationalDataModel?Basedontheconceptofrelations(tablesofdata)RelationshipsestablishedbymatchingprimaryandforeignkeysRelationalDBMSs(RDBMS)arethemostcommonlyusedinindustrytoday.ManyDBMSvendorshavebegunaddi
5、ngobject-orientedfeatures,creatinganobject-relationalmodel.7©PrenticeHall,2007WhatIsaRelation?Anamed,two-dimensionaltablewiththefollowingproperties:Allcellscontainareatomic(single-value)data.Entriesincolumnsarefromthesamesetofvalues(domainrange).Eachrowisunique(i.e.hasanonempt
6、yprimarykey).Columnorderdoesnotmatter.Roworderdoesnotmatter.ThisiscalledFirstNormalForm(1NF)8©PrenticeHall,2007Examplerelation:noteuniquenessofrowsguaranteedbyEmp_ID.Primarykeysareunderlined9©PrenticeHall,2007WhatIsNormalization?Theprocessofconvertingcomplexdatastructuresintow
7、ell-structuredrelationsWell-structuredrelation–arelationthatcontainsaminimumamountofredundanciesandallowsrowstobeinserted,modified,anddeletedwithoutintroducingerrorsorinconsistencies10©PrenticeHall,2007ConsequencesofRelationsthatAreNotWellStructuredInsertionanomaly–addingnewro
8、wsforcesusertocreateduplicatedataUpdateanomaly–changesinonero
