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1、CH1作业Fillintheblank.1、Adatamodelisanotationfordescribingdataorinformation.Thedescriptiongenerallyconsistsofthreeparts:、、.2、andiscalledtheschemaforthatrelation.3、Whenclearingkey(keys),anattributeorlistofattributesmaybedeclaredor. 4、IfPRIMARYKEYisused,thenattributesinSarenotallowe
2、dtohaveasavaluefortheircomponents.Trueorfalse1、Therelationalmodelisbasedontables.2、SQLvaluecan’tbeNULL.3、Eithersaysthatnotwotuplesoftherelationmayagreeinalltheattribute(s)onthelist.4、NoattributeofaPRIMARYKEYcaneverbeNULLinanytuple.ButattributesdeclaredUNIQUEmayhaveNULL’s,andther
3、emaybeseveraltupleswithNULL.5、LikeHTML,theopeningtaginXMLcanhaveatttribute=valuepairs.Singlechoice.1、Inthefollowingfigure,thereareinstancesoftworelationsthatmightconstitutepartofabankingdatabase.Indicatethefollowing:TheattributesofAccountrelationis.A．acctNo,type,balanceB.acctNo,
4、typeC.acctNo,balanceD.acctNom,type,balance2、Howmanydifferentways(consideringordersoftuplesandattributes)aretheretorepresentarelationinstanceifthatinstancehas:nattributesandmtuples?A.n!m!,B.(n-1)!m!,C.n!(m-1)!,Dn!(m+1)!3、Howmanydifferentways(consideringordersoftuplesandattributes
5、)aretheretorepresentarelationinstanceifthatinstancehas:Fourattributesandfivetuples?A.1440,B.2880,C.576,D7204、Howmanydifferentways(consideringordersoftuplesandattributes)aretheretorepresentarelationinstanceifthatinstancehas:Threeattributesandthreetuples?A.20,B.25,C.36,D48Multiple
6、choice1、Inthefollowingfigure,thereareinstancesoftworelationsthatmightconstitutepartofabankingdatabase.Indicatethefollowing:ThetuplesofAccountrelationare.A.(12345,savings,12000)B.(34567,checking,1000),C.(23456,checking,1000)D.(34567,savings,25)Essayquestion1、Wesuggestedthattherea
7、remanyexamplesofattributesthatarecreatedforthepurposeofservingaskeysofrelations.Givesomeexamples.
