数据库系统基础教程第四章答案解析

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1、SolutionsChapter44.1.14.1.2a)b)c)Incweassumethataphoneandaddresscanonlybelongtoasinglecustomer(1-mrelationshiprepresentedbyarrowintocustomer).d)Indweassumethatanaddresscanonlybelongtoonecustomerandaphonecanexistatonlyoneaddress.Ifthemultiplicityofaboverelationshipswerem-to-n,th

2、eentitysetbecomesweakandthekeyssNoofcustomerswillbeneededaspartofthecompositekeyoftheentityset.Inc&d,weconvertattributesphonesandaddressestoentitysets.Sinceentitysetsoftenbecomerelationsinrelationaldesign,wemustconsidermoreefficientalternatives.Insteadofqueryingmultipletableswh

3、erekeyvaluesareduplicated,wecanalsomodifyattributes:(i)PhonesattributecanbeconvertedintoHomePhone,OfficePhoneandCellPhone.(ii)Amultivaluedattributesuchasaliascanbekeptasanattributewhereasinglecolumncanbeusedinrelationaldesigni.e.concatenateallvalues.SQLallowsaquery"like'%Junius

4、%'"tosearchthemultiplevaluesinacolumnalias.4.1.34.1.4a)b)c)Therelationship"played"betweenTeamsandPlayersissimilartorelationship"plays"betweenTeamsandPlayers.4.1.54.1.6TheinformationaboutchildrencanbeascertainedfrommotherOfandfatherOfrelationships.AttributessNoisrequiredsincenam

5、esarenotunique.4.1.74.1.8a)(b)4.1.9AssumptionsAProfessoronlyworksinatmostonedepartment.AcoursehasatmostoneTA.Acourseisonlytaughtbyoneprofessorandofferedbyonedepartment.Studentsandprofessorshavebeenassigneduniqueemailids.Acourseisuniquelyidentifiedbythecourseno,sectionno,andseme

6、ster(e.g.cs157-3spring09).4.1.10Giventhatforeachmovie,auniquestudioexiststhatproducesthemovie.Eachstariscontractedtoatmostonestudio.Butstarscouldbeunemployedatagiventime.Thusthefour-wayrelationshipinfig4.6canbeeasilyintoconvertedequivalentrelationships.4.2.1Redundancy:Theownera

7、ddressisrepeatedinAccSetsandAddressesentitysets.Simplicity:AccSetsdoesnotserveanyusefulpurposeandthedesigncanbemoresimplyrepresentedbycreatingmany-to-manyrelationshipbetweenCustomersandAccounts.Rightkindofelement:TheentitysetAddresseshasasingleattributeaddress.Acustomercannotha

8、vemorethanoneaddress.Henceaddressshouldbeanattributeof