大数据库系统基础教程ch4

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1、实用文档数据库系统基础教程答案ch44.1.14.1.2a)b)文案大全实用文档c)Incweassumethataphoneandaddresscanonlybelongtoasinglecustomer(1-mrelationshiprepresentedbyarrowintocustomer).文案大全实用文档d)Indweassumethatanaddresscanonlybelongtoonecustomerandaphonecanexistatonlyoneaddress.Ifthemultiplicityo

2、faboverelationshipswerem-to-n,theentitysetbecomesweakandthekeyssNoofcustomerswillbeneededaspartofthecompositekeyoftheentityset.Inc&d,weconvertattributesphonesandaddressestoentitysets.Sinceentitysetsoftenbecomerelationsinrelationaldesign,wemustconsidermoreefficien

3、talternatives.Insteadofqueryingmultipletableswherekeyvaluesareduplicated,wecanalsomodifyattributes:(i)PhonesattributecanbeconvertedintoHomePhone,OfficePhoneandCellPhone.(ii)Amultivaluedattributesuchasaliascanbekeptasanattributewhereasinglecolumncanbeusedinrelatio

4、naldesigni.e.concatenateallvalues.SQLallowsaquery"like'%Junius%'"tosearchthemultiplevaluesinacolumnalias.文案大全实用文档4.1.34.1.4a)文案大全实用文档b)c)Therelationship"played"betweenTeamsandPlayersissimilartorelationship"plays"betweenTeamsandPlayers.4.1.5文案大全实用文档4.1.6Theinforma

5、tionaboutchildrencanbeascertainedfrommotherOfandfatherOfrelationships.AttributessNoisrequiredsincenamesarenotunique.文案大全实用文档4.1.7文案大全实用文档4.1.8a)(b)文案大全实用文档4.1.9AssumptionsAProfessoronlyworksinatmostonedepartment.AcoursehasatmostoneTA.Acourseisonlytaughtbyoneprofe

6、ssorandofferedbyonedepartment.Studentsandprofessorshavebeenassigneduniqueemailids.Acourseisuniquelyidentifiedbythecourseno,sectionno,andsemester(e.g.cs157-3spring09).文案大全实用文档4.1.10Giventhatforeachmovie,auniquestudioexiststhatproducesthemovie.Eachstariscontractedt

7、oatmostonestudio.Butstarscouldbeunemployedatagiventime.Thusthefour-wayrelationshipinfig4.6canbeeasilyintoconvertedequivalentrelationships.文案大全实用文档4.2.1Redundancy:TheowneraddressisrepeatedinAccSetsandAddressesentitysets.Simplicity:AccSetsdoesnotserveanyusefulpurpo

8、seandthedesigncanbemoresimplyrepresentedbycreatingmany-to-manyrelationshipbetweenCustomersandAccounts.文案大全实用文档Rightkindofelement:TheentitysetAddresseshasasingl