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1、Exercise3.1.1Answersforthisexercisemayvarybecauseofdifferentinterpretations.SomepossibleFDs:SocialSecuritynumberànameAreacodeàstateStreetaddress,city,stateàzipcodePossiblekeys:{SocialSecuritynumber,streetaddress,city,state,areacode,phonenumber}Needstreetaddress,city,
2、statetouniquelydeterminelocation.Apersoncouldhavemultipleaddresses.Thesameistrueforphones.Thesedays,apersoncouldhavealandlineandacellularphoneExercise3.1.2AnswersforthisexercisemayvarybecauseofdifferentinterpretationsSomepossibleFDs:IDàx-position,y-position,z-positio
3、nIDàx-velocity,y-velocity,z-velocityx-position,y-position,z-positionàIDPossiblekeys:{ID}{x-position,y-position,z-position}Thereasonwhythepositionswouldbeakeyisnotwomoleculescanoccupythesamepoint.Exercise3.1.3aThesuperkeysareanysubsetthatcontainsA1.Thus,thereare2(n-1)
4、suchsubsets,sinceeachofthen-1attributesA2throughAnmayindependentlybechoseninorout.Exercise3.1.3bThesuperkeysareanysubsetthatcontainsA1orA2.Thereare2(n-1)suchsubsetswhenconsideringA1andthen-1attributesA2throughAn.Thereare2(n-2)suchsubsetswhenconsideringA2andthen-2attr
5、ibutesA3throughAn.WedonotcountA1inthesesubsetsbecausetheyarealreadycountedinthefirstgroupofsubsets.Thetotalnumberofsubsetsis2(n-1)+2(n-2).Exercise3.1.3cThesuperkeysareanysubsetthatcontains{A1,A2}or{A3,A4}.Thereare2(n-2)suchsubsetswhenconsidering{A1,A2}andthen-2attrib
6、utesA3throughAn.Thereare2(n-2)–2(n-4)suchsubsetswhenconsidering{A3,A4}andattributesA5throughAnalongwiththeindividualattributesA1andA2.Wegetthe2(n-4)termbecausewehavetodiscardthesubsetsthatcontainthekey{A1,A2}toavoiddoublecounting.Thetotalnumberofsubsetsis2(n-2)+2(n-2
7、)–2(n-4).Exercise3.1.3dThesuperkeysareanysubsetthatcontains{A1,A2}or{A1,A3}.Thereare2(n-2)suchsubsetswhenconsidering{A1,A2}andthen-2attributesA3throughAn.Thereare2(n-3)suchsubsetswhenconsidering{A1,A3}andthen-3attributesA4throughAnWedonotcountA2inthesesubsetsbecauset
8、heyarealreadycountedinthefirstgroupofsubsets.Thetotalnumberofsubsetsis2(n-2)+2(n-3).Exercise3.2.1aWecouldtryinferencerulestodeducen
