数据库系统基础教程答案ch.doc

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1、.数据库系统基础教程答案ch44.1.14.1.2a)b)..c)Incweassumethataphoneandaddresscanonlybelongtoasinglecustomer(1-mrelationshiprepresentedbyarrowintocustomer)...d)Indweassumethatanaddresscanonlybelongtoonecustomerandaphonecanexistatonlyoneaddress.Ifthemultiplicityofaboverelationshipswerem-to-n,theentit

2、ysetbecomesweakandthekeyssNoofcustomerswillbeneededaspartofthecompositekeyoftheentityset.Inc&d,weconvertattributesphonesandaddressestoentitysets.Sinceentitysetsoftenbecomerelationsinrelationaldesign,wemustconsidermoreefficientalternatives.Insteadofqueryingmultipletableswherekeyvaluesar

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

4、valuesinacolumnalias...4.1.34.1.4a)..b)c)Therelationship"played"betweenTeamsandPlayersissimilartorelationship"plays"betweenTeamsandPlayers.4.1.5..4.1.6TheinformationaboutchildrencanbeascertainedfrommotherOfandfatherOfrelationships.AttributessNoisrequiredsincenamesarenotunique...4.1.7..

5、4.1.8a)(b)..4.1.9AssumptionsAProfessoronlyworksinatmostonedepartment.AcoursehasatmostoneTA.Acourseisonlytaughtbyoneprofessorandofferedbyonedepartment.Studentsandprofessorshavebeenassigneduniqueemailids.Acourseisuniquelyidentifiedbythecourseno,sectionno,andsemester(e.g.cs157-3spring09).

6、..4.1.10Giventhatforeachmovie,auniquestudioexiststhatproducesthemovie.Eachstariscontractedtoatmostonestudio.Butstarscouldbeunemployedatagiventime.Thusthefour-wayrelationshipinfig4.6canbeeasilyintoconvertedequivalentrelationships...4.2.1Redundancy:TheowneraddressisrepeatedinAccSetsandAd

7、dressesentitysets.Simplicity:AccSetsdoesnotserveanyusefulpurposeandthedesigncanbemoresimplyrepresentedbycreatingmany-to-manyrelationshipbetweenCustomersandAccounts...Rightkindofelement:TheentitysetAddresseshasasingleattributeaddress.Acustomercannothavemorethanoneaddress.Henceaddresss