数据库系统基础教程课后答案第四章

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

2、n,theentitysetbecomesweakandthekeyssNoofcustomerswillbeneededaspartofthecompositekeyoftheentityset.Inc&d,weconvertattributesphonesandaddressestoentitysets.Sinceentitysetsoftenbecomerelationsinrelationaldesign,wemustconsidermoreefficientalternatives.Insteadofqueryingmultiple

3、tableswherekeyvaluesareduplicated,wecanalsomodifyattributes:(i)PhonesattributecanbeconvertedintoHomePhone,OfficePhoneandCellPhone.(ii)Amultivaluedattributesuchasaliascanbekeptasanattributewhereasinglecolumncanbeusedinrelationaldesigni.e.concatenateallvalues.SQLallowsaquery"

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

5、requiredsincenamesarenotunique.4.1.74.1.8a)(b)4.1.9AssumptionsAProfessoronlyworksinatmostonedepartment.AcoursehasatmostoneTA.Acourseisonlytaughtbyoneprofessorandofferedbyonedepartment.Studentsandprofessorshavebeenassigneduniqueemailids.Acourseisuniquelyidentifiedbythecourse

6、no,sectionno,andsemester(e.g.cs157-3spring09).4.1.10Giventhatforeachmovie,auniquestudioexiststhatproducesthemovie.Eachstariscontractedtoatmostonestudio.Butstarscouldbeunemployedatagiventime.Thusthefour-wayrelationshipinfig4.6canbeeasilyintoconvertedequivalentrelationships.4

7、.2.1Redundancy:TheowneraddressisrepeatedinAccSetsandAddressesentitysets.Simplicity:AccSetsdoesnotserveanyusefulpurposeandthedesigncanbemoresimplyrepresentedbycreatingmany-to-manyrelationshipbetweenCustomersandAccounts.Rightkindofelement:TheentitysetAddresseshasasingleattrib

8、uteaddress.Acustomercannothavemorethanoneaddress.Henceaddressshouldbeanattributeof