数据库期末考试题

1.DBMShasmanyadvantages.Thenwhataretwodisadvantagesofdatabasesystem?

Answer:Twodisadvantagesassociatedwithdatabasesystemsarelisted

below.

a.Setupofthedatabasesystemrequiresmoreknowledge,money,skills,

andtime.

b.b.Thecomplexityofthedatabasemayresultinpoorperformance.

2Listfiveresponsibilitiesofadatabasemanagementsystem.

Ansers:

eractionwiththefilemanager.

egrityenforcement.

c.securityenforcement.

d.backupandrecovery.

e.concurrencycontrol.

3.Whatarefivemainfunctionsofadatabaseadministrator?

Answer:Fivemainfunctionsofadatabaseadministratorare:

,Tbcreatetheschemedefinition

,Todefinethestoragestructureandaccessmethods

,Tbmodifytheschemeand/orphysicalorganizationwhennecessary

,Tograntauthorizationfordataaccess

,Tospecifyintegrityconstraints

4.Explainthedistinctionsamongthetermsprimarykey,candidatekey,

andsuperkey.

Answer:Asuperkeyisasetofoneormoreattributesthat,taken

collectively,al-lowsustoidentifyuniquelyanentityintheentityset.A

superkeymaycontainextraneousattributes.IfKisasuperkey,thensois

anysupersetofK.Asuperkeyforwhichnopropersubsetisalsoa

superkeyiscalledacandidatekey.Itispossiblethatseveraldistinctsets

ofattributescouldserveascandidatekeys.Theprimarykeyisoneofthe

candidatekeysthatischosenbythedatabasedesignerastheprincipal

meansofidentifyingentitieswithinanentityset

6.Whatislogicaldataindependenceandwhyisitimportant?

Answer:Logicaldataindependencemeansthatusersareshieldedfrom

changesinthelogicalstructureofthedata,i.e.,changesinthechoiceof

relationstobestored.Forexample,ifarelationStudents(sid,sname,gpa)

isreplacedbyStudentnames(sid,sname)andStudentgpas(sid,gpa)for

somereason,applicationprogramsthatoperateontheStudentsrelation

canbeshieldedfromthischangebydefiningaviewStu-dents(sid,sname,

gpa)(asthenaturaljoinofStudentnamesandStudentgpas).Thus,

applicationprogramsthatrefertoStudentsneednotbechangedwhenthe

relationStudentsisreplacedbytheothertworelations.Theonlychange

isthatinsteadofstoringStudentstuples,thesetuplesarecomputedas

neededbyusingtheviewdefinition;thisistransparenttotheapplication

program.

7.Whichofthefollowingplaysanimportantroleinrepresentinginforma

tionabouttherealworldinadatabase?Explainbriefly.

1.Thedatadefinitionlanguage.

2.Thedatamanipulationlanguage.

3.Thebuffermanager.

4.Thedatamodel.

8Considerthefollowinginformationaboutauniversitydatabase:

ProfessorshaveanSSN,aname,anage,arank,andaresearchspecialty.

Projectshaveaprojectnumber,asponsorname(e.g.,NSF),astarting

date,anendingdate,andabudget.

GraduatestudentshaveanSSN,aname,anage,andadegreeprogram

(e.g.,M.S.orPh.D.).

Eachprojectismanagedbyoneprofessor(knownastheproject's

principalinvestigator).

Eachprojectisworkedonbyoneormoreprofessors(knownasthe

project'sco-investigators).

Professorscanmanageand/orworkonmultipleprojects.

Eachprojectisworkedonbyoneormoregraduatestudents(knownas

theproject'sresearchassistants).

Whengraduatestudentsworkonaproject,aprofessormustsupervise

theirworkontheproject.Graduatestudentscanworkonmultiple

projects,inwhichcasetheywillhavea(potentiallydifferent)supervisor

foreachone.

Departmentshaveadepartmentnumber,adepartmentname,andamain

office.

Departmentshaveaprofessor(knownasthechairman)whorunsthe

department.

Professorsworkinoneormoredepartments,andforeachdepartmentthat

theyworkin,atimepercentageisassociatedwiththeirjob.

Graduatestudentshaveonemajordepartmentinwhichtheyareworking

ontheirdegree.

Eachgraduatestudenthasanother,moreseniorgraduatestudent(known

asastudentadvisor)whoadviseshimorheronwhatcoursestotake.

DesignanddrawanERdiagramthatcapturestheinformationaboutthe

university.

UseonlythebasicERmodelhere;thatis,entities,relationships,and

attributes.Besuretoindicateanykeyandparticipationconstraints.

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dnameCHAR(64),

officeCHAR(IO),

PRIMARYKEY(dno))

3.CREATETABLERuns(dnoINTEGER,

profssnCHAR(IO),

PRIMARYKEY(dno,profssn),

FOREIGNKEY(profssn)REFERENCESProfessors,

FOREIGNKEY(dno)REFERENCESDepts)

4.CREATETABLEWorkDept(dnoINTEGER,

profssnCHAR(IO),

pctimeINTEGER,

PRIMARYKEY(dno,profssn),

FOREIGNKEY(profssn)REFERENCESProfessors,

FOREIGNKEY(dno)REFERENCESDepts)

ObservethatwewouldneedcheckconstraintsorassertionsinSQLto

enforcetherulethatProfessorsworkinatleastonedepartment.

5.CREATETABLEProject(pidINTEGER,

sponsorCHAR(32),

startdateDATE,

enddateDATE,

budgetFLOAT,

PRIMARYKEY(pid))

6.CREATETABLEGraduates(gradssnCHAR(IO),

ageINTEGER,

nameCHAR(64),

degprogCHAR(32),

majorINTEGER,

PRIMARYKEY(gradssn),

FOREIGNKEY(major)REFERENCESDepts)

NotethattheMajortableisnotnecessarysinceeachGraduatehasonly

onemajor

andsothiscanbeanattributeintheGraduatestable.

7.CREATETABLEAdvisor(seniorssnCHAR(IO),

gradssnCHAR(IO),

PRIMARYKEY(seniorssn,gradssn),

FOREIGNKEY(seniorssn)

REFERENCESGraduates(gradssn),

FOREIGNKEY(gradssn)REFERENCESGraduates)

8.CREATETABLEManages(pidINTEGER,

profssnCHAR(IO),

PRIMARYKEY(pid,profssn),

FOREIGNKEY(profssn)REFERENCESProfessors,

FOREIGNKEY(pid)REFERENCESProjects)

9.CREATETABLEWorkIn(pidINTEGER,

profssnCHAR(IO),

PRIMARYKEY(pid,profssn),

FOREIGNKEY(profssn)REFERENCESProfessors,

FOREIGNKEY(pid)REFERENCESProjects)

ObservethatwecannotenforcetheparticipationconstraintforProjectsin

the

WorkIntablewithoutcheckconstraintsorassertionsinSQL.

10.CREATETABLESupervises(profssnCHAR(10),

gradssnCHAR(10),

pidINTEGER,

PRIMARYKEY(profssn,gradssn,pid),

FOREIGNKEY(profssn)REFERENCESProfessors,

FOREIGNKEY(gradssn)REFERENCESGraduates,

FOREIGNKEY(pid)REFERENCESProjects)

NotethatwedonotneedanexplicittablefortheWorkProjrelationsince

everytimeaGraduateworksonaProject,heorshemusthavea

Supervisor.

10.Considerthefollowingrelations:

Student(snum:integer,sname:string,major:string,level:string,age:

integer)

Class(name:string,meetsat:string,room:string,fid:integer)

Enrolled(snum:integer,cname:string)

Faculty(fid:integer,fhame:string,deptid:integer)

Themeaningoftheserelationsisstraightforward;forexample,Enrolled

hasonerecordperstudent-classpairsuchthatthestudentisenrolledin

theclass.

WritethefollowingqueriesinSQL.Noduplicatesshouldbeprintedin

anyoftheanswers.

1.FindthenamesofallJuniors(level=JR)whoareenrolledinaclass

taughtbyI.leach.

2.FindtheageoftheoldeststudentwhoiseitheraHistorymajoror

enrolledinacoursetaughtbyI.Teach.

3.FindthenamesofallclassesthateithermeetinroomRI28orhave

fiveormorestudentsenrolled.

4.Findthenamesofallstudentswhoareenrolledintwoclassesthat

meetatthesametime.

5.Findthenamesoffacultymemberswhoteachineveryroominwhich

someclassistaught.

Theanswersaregivenbelow:

1.SELECTDISTINCTS.Sname

FROMStudentS,ClassC,EnrolledE,FacultyF

WHERES.snum=E.snumANDE.cname=C.nameAND6d=F.fid

AND

F.fname='I.Teach'ANDS.level='JR'

2.SELECTMAX(S.age)

FROMStudentS

WHERE(S.major='History')

ORS.snumIN(SELECTE.snum

FROMClassC,EnrolledE,FacultyF

WHEREE.cname=C.nameANDC.fid=F.fid

ANDF.fname=工Teach')

3.SELECTC.name

FROMClassC

WHEREC.room='R128'

ORC.nameIN(SELECTE.cname

FROMEnrolledE

GROUPBYE.cname

HAVINGCOUNT(*)>=5)

4.SELECTDISTINCTS.sname

FROMStudentS

WHERES.snumIN(SELECTEl.snum

FROMEnrolledEl,EnrolledE2,ClassCl,ClassC2

WHEREEl.snum=E2.snumANDEame<>E2.cname

ANDEame=C

ANDE2.cname=C2.nameANDCl.meetsat=C2.meetsat)

5.SELECTDISTINCTEfname

FROMFacultyF

WHERENOTEXISTS((SELECT*

FROMClassC)

EXCEPT

(SELECTCI.room

FROMClassCl

WHEREC1.fid=F.fid))

l.Listfoursignficantdifferencesbetweenafile-processingsystemandaDBMS.

Answer:Somemaindifferencesbetweenadatabasemanagementsystemand

afile-processingsystemare:

•Bothsystemscontainacollectionofdataandasetofprogramswhichaccessthatdata.A

databasemanagementsystemcoordinatesboththephysicalandthelogicalaccesstothedata,

whereasafile-processingsystemcoordinatesonlythephysicalaccess.

•Adatabasemanagementsystemreducestheamountofdataduplicationby

ensuringthataphysicalpieceofdataisavailabletoallprogramsauthorized

tohaveaccesstoit,whereasdatawrittenbyoneprograminfiie-processing

systemmaynotbereadablebyanotherprogram.

•Adatabasemanagementsystemisdesignedtoallowflexibleaccesstodata

(i.e.,queries),whereasafile-processingsystemisdesignedtoallowpredeterminedaccesstodata

(i.e.,compiledprograms).

•Adatabasemanagementsystemisdesignedtocoordinatemultipleusers

accessingthesamedataatthesametime.Afile-processingsystemisusually

designedtoallowoneormoreprogramstoaccessdifferentdafiiesat

thesametime.Inafile-processingsystem,afilecanbeaccessedbytwo

programsconcuiTentlyonlyifbothprogramshaveread-onlyaccesstothe

file.

2Whywouldyouchooseadatabasesysteminsteadofsimplystoringdata

inoperatingsystemfiles?Whenwoulditmakesensenottouseadatabasesystem?

Answer1.1Adatabaseisanintegratedcollectionofdata,usuallysolargethatit

hastobestoredonsecondarystoragedevicessuchasdisksortapes.Thisdatacan

bemaintainedasacollectionofoperatingsysteifiles,orstoredinaDBMS(database

managementsystem).TheadvantagesofusingaDBMSare:

Dataindependenceandefficientaccess.Databaseapplicationprogramsarein­

dependentofthedetailsofdatarepresentationandstorage.Theconceptualand

externalschemasprovideindependencefromphysicalstoragedecisionsandlogical

designdecisionsrespectively.Inaddition,aDBMSprovidesefficientstorageand

retrievalmechanisms,includingsupportforverylarries,indexstructuresand

queryoptimization.

Reducedapplicationdevelopmenttime.SincetheDBMSprovidesseveralimpor­

tantfunctionsrequiredbyapplications,suchasconcurrencycontrolandcrash

recovery,highlevelqueryfacilities,etc.,onlyapplication-specificcodeneedsto

bewritten.Eventhisisfacilitatedbysuitesofapplicationdevelopmenttools

availablefromvendorsformanydatabasemanagementsystems.

Dataintegrityandsecurity.Theviewmechanismandtheauthorizationfacilities

ofaDBMSprovideapowerfulaccesscontrolmechanism.Further,updatestothe

datathatviolatethesemanticsofthedatacanbedetectedandrejectedbythe

DBMSifusersspecifytheappropriateintegrityconstraints.

Dataadministration.Byprovidingacommonumbrellaforalargecollectionof

datathatissharedbyseveralusers,aDBMSfacilitatesmaintenanceanddata

administrationtasks.AgoodDBAcaneffectivelyshieldend-usersfromthechores

offine-tuningthedatarepresentation,periodicback-upsetc.

Concurrentaccessandcrashrecovery.ADBMSsupportsthenotionofatrans­

action,whichisconceptuallyasingleuser'ssequentialprogram.Userscanwrite

transactionsasiftheirprogramswererunninginisolationagainstthedatabase.

TheDBMSexecutestheactionsoftransactionsinaninterleavedfashiontoobtain

goodperformance,butschedulestheminsuchawayastoensurethatcflicting

operationsarenotpermittedtoproceedconcurrently.Further,theDBMSmain­

tainsacontinuouslogofthechangestothedata,andifthereisasystemcrash,

itcanrestorethedatabasetoatransaction-consistentstate.Thatis,theactions

ofincompletetransactionsareundone,sothatthedatabasestateftectsonlythe

actionsofcompletedtransactions.Thus,ifeachcompletetransaction,executing

alone,maintainstheconsistencycriteria,thenthedatabasestateafterrecovery

fromacrashisconsistent.

Iftheseadvantagesarenotimportantfortheapplicationathand,usingacollectionof

filesmaybeabettersolutionbecauseoftheincreasedcostandoverheadofpurchasingand

maintainingaDBMS.

3.Whatislogicaldataindependenceandwhyisitimportant?

Answer1.2Logicaldataindependencemeansthatusersareshieldedfromchangesin

thelogicalstructureofthedata,i.e.,changesinthechoiceofrelationstobestored.

Forexample,ifarelationStudents(sid,sname,gpa)isreplacedbyStudentnames(sid,

sname)andStudentgpas(sid,gpa)forsomereason,applicationprogramsthatoperate

ontheStudentsrelationcanbeshieldedfromthischangeby(fciingaviewStu-

dents(sid,sname,gpa)(asthenaturaljoinofStudentnamesandStudentgpas).Thus,

applicationprogramsthatrefertoStudentsneednotbechangedwhentherelationStudentsis

replacedbytheothertworelations.TheonlychangeisthatinsteadofstoringStudentstuples,

thesetuplesarecomputedasneededbyusingtheyficntiafethisistransparenttothe

applicationprogram.

Exercise1.5WhataretheresponsibilitiesofaDBA?

Answer1.5TheDBAisresponsiblefor:

Designingthelogicalandphysicalschemas,aswellaswidely-usedportionsofthe

externalschema.

Securityandauthorization.

Dataavailabilityandrecoveryfromfailures.

Databasetuning:TheDBAisresponsibleforevolvingthedatabase,inparticular

theconceptualandphysicalschemas,toensureadequateperformanceasuser

requirementschange.

Answer1.7Letusdiscussthechoicesinturn.

Thedatadefinitionlanguageisimportantinrepresentinginformationbecauseit

isusedtodescribeexternalandlogicalschemas.

Thedatamanipulationlanguageisusedtoaccessandupdatedata;itisnot

importantforrepresentingthedata.(Ofcourse,thedatamanipulationlanguage

mustbeawareofhowdataisrepresented,anditectsthisintheconstructsthat

itsupports.)

Thebuffermanagerisnotveryimportantforrepresentationbecauseitbrings

arbitrarydiskpagesintomainmemory,independentofanydatarepresentation.

Thedatamodelisfundamentaltorepresentinginformation.Thedatamodel

determineswhatdatarepresentationmechanismsaresupportedbytheDBMS.

Thedatadefinitionlanguageisjustthespecificsetoflanguageconstructsavailable

todescribeanactualapplication'sdataintermsofthedatamodel.

Exercise2.4Acompanydatabaseneedstostoreinformationaboutemployeefie^cteyiti

ssn,withsalaryandphoneasattributes),departments(ideiftcdbydno,withdnameandbudgetas

attributes),andchildrenofemployees(withnameandageasattributes).Employeesworkin

departments;eachdepartmentismanagedbyanemployee;achildmustbeidenfieduniquelyby

namewhentheparent(whoisanemployee;assumethatonlyoneparentworksfbrthecompany)

isknown.Wearenotinterestedininformationaboutachildoncetheparentleavesthecompany.

DrawanERdiagramthatcapturesthisinformation.

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Exercise3.14ConsiderthescenariofromExercise2.4,whereyoudesignedanER

diagramfbracompanydatabase.WriteSQLstatementstocreatethecorresponding

relationsandcaptureasmanyoftheconstraintsaspossible.Ifyoucannotcapture

someconstraints,explainwhy.

Answer3.14ThefollowingSQLstatementscreatethecorrespondingrelations.

CREATETABLEEmployees(ssnCHAR(IO),

salINTEGER,

phoneCHAR(13),

PRIMARYKEY(ssn))

CREATETABLEDepartments(dnoINTEGER,

budgetINTEGER,

dnameCHAR(20),

PRIMARYKEY(dno))

CREATETABLEWorksin(ssnCHAR(IO),

dnoINTEGER,

PRIMARYKEY(ssn,dno),

FOREIGNKEY(ssn)REFERENCESEmployees,

FOREIGNKEY(dno)REFERENCESDepartments)

CREATETABLEManages(ssnCHAR(IO),

dnoINTEGER,

PRIMARYKEY(dno),

FOREIGNKEY(ssn)REFERENCESEmployees,

FOREIGNKEY(dno)REFERENCESDepartments)

CREATETABLEDependents(ssnCHAR(10),

nameCHAR(10),

ageINTEGER,

PRIMARYKEY(ssn,name),

FOREIGNKEY(ssn)REFERENCESEmployees,

ONDELETECASCADE)

Exercise5.1Considerthefollowingrelations:

Student(snum:integer,sname:string,major:string,level:string,age:integer)

Class(name:string,meetsat:string,room:stringd:integer)

Enrolled(snum:integer,cname:string)

Faculty(fid:integer,fname:string,deptid:integer)

Themeaningoftheserelationsisstraightforward;forexample,Enrolledhasonerecordper

student-classpairsuchthatthestudentisenrolledintheclass.

WritethefollowingqueriesinSQL.Noduplicatesshouldbeprintedinanyoftheanswers.

1.Findthenamesoffacultymembersforwhomthecombinedenrollmentofthecoursesthatthey

teachislessthanfive.

2.Foreachlevel,printthelevelandtheaverageageofstudentsforthatlevel.

3.ForalllevelsexceptJR,printthelevelandtheaverageageofstudentsforthatlevel.

4.ForeachfacultymemberthathastaughtclassesonlyinroomR128,printthefacultymember's

nameandthetotalnumberofclassessheorhehastaught.

5.Findthenamesofstudentsenrolledinthemaximumnumberofclasses.

6.Findthenamesofstudentsnotenrolledinanyclass.

1.SELECTDISTINCTF.fname

FROMFacultyF

WHERE5>(SELECTCOUNT(E.snum)

FROMClassC,EnrolledE

WHEREC.name=E.cname

ANDC.fid=F.fid)

2.SELECTS.level,AVG(S.age)

FROMStudentS

GROUPBYS.level

3.SELECTS.level,AVG(S.age)

FROMStudentS

WHERES.levelo，JR'

GROUPBYS.level

4.SELECTF.fname,COUNT(*)ASCourseCount

FROMFacultyF,ClassC

WHEREF.fid=C.fid

GROUPBYF.fid,F.fname

HAVINGEVERY(C.room='R128')

5.SELECTDISTINCTS.sname

FROMStudentS

WHERES.snumIN(SELECTE.snum

FROMEnrolledE

GROUPBYE.snum

HAVINGCOUNT(*)>=ALL(SELECTCOUNT(*)

FROMEnrolledE2

GROUPBYE2.snum))

6.SELECTDISTINCTS.sname

FROMStudentS

WHERES.snumNOTIN(SELECTE.snum

FROMEnrolledE)

1.1.ExplainthefollowingtermsIftjeattribute,domain,entity,relationship,one-to-many

relationship,many-to-manyrelationship.

Answer2.1Termexplanations:

Attribute-apropertyordescriptionofanentity.Atoydepartmentemployee

entitycouldhaveattributesdescribingtheemployee\name,salary,andyearsof

service.

Domain-asetofpossiblevaluesforanattribute.

Entity-anobjectintherealworldthatisdistinguishablefromotherobjectssuch

asthegreendragontoy.

Relationship-anassociationamongtwoormoreentities.

Entityset-acollectionofsimilarentitiessuchasallofthetoysinthetoydepart­

ment.

Relationshipset-acollectionofsimilarrelationships

One-to-manyrelationship-akeyconstraintthatindicatesthatoneentitycanbe

associatedwithmanyofanotherentity.Anexampleofaone-to-manyrelationship

iswhenanemployeecanworkforonlyonedepartment,andadepartmentcan

havemanyemployees.

Many-to-manyrelationship-akeyconstraintthatindicatesthatmanyofone

entitycanbeassociatedwithmanyofanotherentity.Anexampleofamany-

to-manyrelationshipisemployeesandtheirhobbies:apersoncanhavemany

differenthobbies,andmanypeoplecanhavethesamehobby.

2.Exercise4.2GiventworelationsRIandR2,whereRIcontainsN1tuples,R2con-

tainsN2tuples,andN2>N1>0,givetheminimumandmaximumpossiblesizes(in

tuples)fortheresultingrelationproducedbyeachofthefollowingrelationalalgebra

expressions.Ineachcase,stateanyassumptionsabouttheschemasforR1andR2

neededtomaketheexpressionmeaningful:

(1)R1UR2,(2)RinR2,(3)R1-R2,(4)RlxR2,(5)oa=5(R1),(6)Tra(Rl),

and(7)R1/R2

Aanswer:

ExpressionAssumptionMinMax

R1UR2RIand7?2areunion-compatibleN2N1+N2

Rir\R2RIandR2areunion-compatibleiiN1

R1-H2RIandR2areunion-compatibleiiN1

RIxR2N1*N2N1*N2

Oa=5(Hl)Hlhasanattributenameda(jXI

ira(Rl)RIhasattributea.Nl>01X.

ThesetofattributesofR2isa

R1/R2subsetofthesetofattributesof00

Hl

ThesetofattributesofR\isa

R2JR1subsetofthesetofattributesof0LN2/N1J

R2

Figure4.1AnswertoExercise4.2.

Exercise2.5NotownRecordshasdecidedtostoreinformationaboutmusicianswho

performonitsalbums(aswellasothercompanydata)inadatabase.Thecompany

haswiselychosentohireyouasadatabasedesigner(atyourusualconsultingfeeof

$2500/day).

EachmusicianthatrecordsatNotownhasanSSN,aname,anaddress,and

aphonenumber.Poorlypaidmusiciansoftensharethesameaddress,andno

addresshasmorethanonephone.

EachinstrumentusedinsongsrecordedatNotownhasauniqueidentification

number,aname(eg,guitar,synthesizerflute)andamusicalkey(e.g.,C,B-flat,

E-flat).

EachalbumrecordedontheNotownlabelhasauniqueideiftcationnumber,a

title,acopyrightdate,aformat(e.g.,CDorMC),andanalbumidentifier.

EachsongrecordedatNotownhasatitleandanauthor.

Eachmusicianmayplayseveralinstruments,andagiveninstrumentmaybe

playedbyseveralmusicians.

Eachalbumhasanumberofsongsonit,butnosongmayappearonmorethan

onealbum.

Eachsongisperformedbyoneormoremusicians,andamusicianmayperforma

numberofsongs.

Eachalbumhasexactlyonemusicianwhoactsasitsproducer.Amusicianmay

produceseveralalbums,ofcourse.

Designaconceptualschemaf