數(shù)據(jù)庫系統(tǒng)基礎(chǔ)教程第三章答案_第1頁
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1、ExerciseExercise3.1.13.1.1Answersfthisexercisemayvarybecauseofdifferentinterpretations.SomepossibleFDs:SocialSecuritynumber?nameAreacode?stateStreetaddresscitystate?zipcodePossiblekeys:SocialSecuritynumberstreetaddressci

2、tystateareacodephonenumberNeedstreetaddresscitystatetouniquelydeterminelocation.Apersoncouldhavemultipleaddresses.Thesameistruefphones.ThesedaysapersoncouldhaveallineacellularphoneExerciseExercise3.1.23.1.2Answersfthisex

3、ercisemayvarybecauseofdifferentinterpretationsSomepossibleFDs:ID?xpositionypositionzpositionID?xvelocityyvelocityzvelocityxpositionypositionzposition?IDPossiblekeys:IDxpositionypositionzpositionThereasonwhythepositionswo

4、uldbeakeyisnotwomoleculescanoccupythesamepoint.ExerciseExercise3.1.3a3.1.3aThesuperkeysareanysubsetthatcontainsA1.Thusthereare2(n1)suchsubsetssinceeachofthen1attributesA2throughAnmayindependentlybechoseninout.ExerciseExe

5、rcise3.1.3b3.1.3bThesuperkeysareanysubsetthatcontainsA1A2.Thereare2(n1)suchsubsetswhenconsideringA1then1attributesA2throughAn.Thereare2(n2)suchsubsetswhenconsideringA2then2attributesA3throughAn.WedonotcountA1inthesesubse

6、tsbecausetheyarealreadycountedinthefirstgroupofsubsets.Thetotalnumberofsubsetsis2(n1)2(n2).ExerciseExercise3.1.3c3.1.3cThesuperkeysareallthosethatcontainoneofthosethreekeys.ThatisasuperkeythatisnotakeymustcontainBmethano

7、neofACD.Thusthe(proper)superkeysareABCABDBCDABCD.ExerciseExercise3.2.2a3.2.2ai)FthesingleattributeswehaveA=ABCDB=BCDC=CD=D.ThusthenewdependenciesareA?CA?D.Nowconsiderpairsofattributes:AB=ABCDAC=ABCDAD=ABCDBC=BCDBD=BCDCD=

8、CD.ThusthenewdependenciesareAB?CAB?DAC?BAC?DAD?BAD?CBC?DBD?C.FthetriplesofattributesBCD=BCDbuttheclosuresoftheothersetsareeachABCD.ThuswegetnewdependenciesABC?DABD?CACD?B.SinceABCD=ABCDwegetnonewdependencies.Thecollectio

9、nof13newdependenciesmentionedaboveare:A?CA?DAB?CAB?DAC?BAC?DAD?BAD?CBC?DBD?CABC?DABD?CACD?B.ii)FthesingleattributeswehaveA=AB=BC=CD=D.Thustherearenonewdependencies.Nowconsiderpairsofattributes:AB=ABCDAC=ACAD=ABCDBC=ABCDB

10、D=BDCD=ABCD.ThusthenewdependenciesareAB?DAD?CBC?ACD?B.FthetriplesofattributesalltheclosuresofthesetsareeachABCD.ThuswegetnewdependenciesABC?DABD?CACD?BBCD?A.SinceABCD=ABCDwegetnonewdependencies.Thecollectionof8newdepende

11、nciesmentionedaboveare:AB?DAD?CBC?ACD?BABC?DABD?CACD?BBCD?A.iii)FthesingleattributeswehaveA=ABCDB=ABCDC=ABCDD=ABCD.ThusthenewdependenciesareA?CA?DB?DB?AC?AC?BD?BD?C.Sinceallthesingleattributes’closuresareABCDanysuperseto

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