数据库理论及基础面试题.docx

数据库理论及基础面试题.docx

《数据库理论及基础面试题.docx》由会员分享，可在线阅读，更多相关《数据库理论及基础面试题.docx（20页珍藏版）》请在冰豆网上搜索。

数据库理论及基础面试题

数据库理论及基础面试题

问题：

数据库理论及基础面试题回答：

1.WhatisdatabaseAdatabaseisalogicallycoherentcollectionofdatawithsomeinherentmeaning,representingsomeaspectofrealworldandwhichisdesigned,builtandpopulatedwithdataforaspecificpurpose.

2.WhatisDBMSItisacollectionofprogramsthatenablesusertocreateandmaintainadatabase.Inotherwordsitisgeneral-purposesoftwarethatprovidestheuserswiththeprocessesofdefining,constructingandmanipulatingthedatabaseforvariousapplications.

3.WhatisaDatabasesystemThedatabaseandDBMSsoftwaretogetheriscalledasDatabasesystem.

4.AdvantagesofDBMSRedundancyiscontrolled.Unauthorisedaccessisrestricted.Providingmultipleuserinterfaces.Enforcingintegrityconstraints.Providingbackupandrecovery.

5.DisadvantageinFileProcessingSystemDataredundancyinconsistency.Difficultinaccessingdata.Dataisolation.Dataintegrity.Concurrentaccessisnotpossible.SecurityProblems.

6.DescribethethreelevelsofdataabstractionThearethreelevelsofabstraction:

Physicallevel:

Thelowestlevelofabstractiondescribeshowdataarestored.Logicallevel:

Thenexthigherlevelofabstraction,describeswhatdataarestoredindatabaseandwhatrelationshipamongthosedata.Viewlevel:

Thehighestlevelofabstractiondescribesonlypartofentiredatabase.7.DefinetheintegrityrulesTherearetwoIntegrityrules.

EntityIntegrity:

Statesthat“PrimarykeycannothaveNULLvalue”ReferentialIntegrity:

Statesthat“ForeignKeycanbeeitheraNULLvalueorshouldbePrimaryKeyvalueofotherrelation.

8.WhatisextensionandintensionExtension-

Itisthenumberoftuplespresentinatableatanyinstance.Thisistimedependent.

Intension-

Itisaconstantvaluethatgivesthename,structureoftableandtheconstraintslaidonit.

9.WhatisSystemRWhatareitstwomajorsubsystemsSystemRwasdesignedanddevelopedoveraperiodof1974-79atIBMSanJoseResearchCenter.ItisaprototypeanditspurposewastodemonstratethatitispossibletobuildaRelationalSystemthatcanbeusedinareallifeenvironmenttosolvereallifeproblems,withperformanceatleastcomparabletothatofexistingsystem.

Itstwosubsystemsare

ResearchStorageSystemRelationalDataSystem.

10.HowisthedatastructureofSystemRdifferentfromtherelationalstructureUnlikeRelationalsystemsinSystemR

DomainsarenotsupportedEnforcementofcandidatekeyuniquenessisoptionalEnforcementofentityintegrityisoptionalReferentialintegrityisnotenforced

11.WhatisDataIndependenceDataindependencemeansthat“theapplicationisindependentofthestoragestructureandaccessstrategyofdata”.Inotherwords,Theabilitytomodifytheschemadefinitioninonelevelshouldnotaffecttheschemadefinitioninthenexthigherlevel.

TwotypesofDataIndependence:

PhysicalDataIndependence:

Modificationinphysicallevelshouldnotaffectthelogicallevel.LogicalDataIndependence:

Modificationinlogicallevelshouldaffecttheviewlevel.NOTE:

LogicalDataIndependenceismoredifficulttoachieve

12.WhatisaviewHowitisrelatedtodataindependenceAviewmaybethoughtofasavirtualtable,thatis,atablethatdoesnotreallyexistinitsownrightbutisinsteadderivedfromoneormoreunderlyingbasetable.Inotherwords,thereisnostoredfilethatdirectrepresentstheviewinsteadadefinitionofviewisstoredindatadictionary.

Growthandrestructuringofbasetablesisnotreflectedinviews.Thustheviewcaninsulateusersfromtheeffectsofrestructuringandgrowthinthedatabase.Henceaccountsforlogicaldataindependence.

13.WhatisDataModelAcollectionofconceptualtoolsfordescribingdata,datarelationshipsdatasemanticsandconstraints.

14.WhatisE-RmodelThisdatamodelisbasedonrealworldthatconsistsofbasicobjectscalledentitiesandofrelationshipamongtheseobjects.Entitiesaredescribedinadatabasebyasetofattributes.

15.WhatisObjectOrientedmodelThismodelisbasedoncollectionofobjects.Anobjectcontainsvaluesstoredininstancevariableswithintheobject.Anobjectalsocontainsbodiesofcodethatoperateontheobject.Thesebodiesofcodearecalledmethods.Objectsthatcontainsametypesofvaluesandthesamemethodsaregroupedtogetherintoclasses.

16.WhatisanEntityItisathingintherealworldwithanindependentexistence.

17.WhatisanEntitytypeItisacollection（set）ofentitiesthathavesameattributes.

18.WhatisanEntitysetItisacollectionofallentitiesofparticularentitytypeinthedatabase.

19.WhatisanExtensionofentitytypeThecollectionsofentitiesofaparticularentitytypearegroupedtogetherintoanentityset.

20.WhatisWeakEntitysetAnentitysetmaynothavesufficientattributestoformaprimarykey,anditsprimarykeycompromisesofitspartialkeyandprimarykeyofitsparententity,thenitissaidtobeWeakEntityset.

21.WhatisanattributeItisaparticularproperty,whichdescribestheentity.

22.WhatisaRelationSchemaandaRelationArelationSchemadenotedbyR（A1,A2,…,An）ismadeupoftherelationnameRandthelistofattributesAithatitcontains.Arelationisdefinedasasetoftuples.Letrbetherelationwhichcontainssettuples（t1,t2,t3,,tn）.Eachtupleisanorderedlistofn-valuest=（v1,v2,,vn）.

23.WhatisdegreeofaRelationItisthenumberofattributeofitsrelationschema.

24.WhatisRelationshipItisanassociationamongtwoormoreentities.

25.WhatisRelationshipsetThecollection（orset）ofsimilarrelationships.

26.WhatisRelationshiptypeRelationshiptypedefinesasetofassociationsorarelationshipsetamongagivensetofentitytypes.

27.WhatisdegreeofRelationshiptypeItisthenumberofentitytypeparticipating.

25.WhatisDDL（DataDefinitionLanguage）AdatabaseschemaisspecifiesbyasetofdefinitionsexpressedbyaspeciallanguagecalledDDL.

26.WhatisVDL（ViewDefinitionLanguage）Itspecifiesuserviewsandtheirmappingstotheconceptualschema.

27.WhatisSDL（StorageDefinitionLanguage）Thislanguageistospecifytheinternalschema.Thislanguagemayspecifythemappingbetweentwoschemas.

28.WhatisDataStorageDefinitionLanguageThestoragestructuresandaccessmethodsusedbydatabasesystemarespecifiedbyasetofdefinitioninaspecialtypeofDDLcalleddatastorage-definitionlanguage.

29.WhatisDML（DataManipulationLanguage）Thislanguagethatenableusertoaccessormanipulatedataasorganisedbyappropriatedatamodel.

ProceduralDMLorLowlevel:

DMLrequiresausertospecifywhatdataareneededandhowtogetthosedata.Non-ProceduralDMLorHighlevel:

DMLrequiresausertospecifywhatdataareneededwithoutspecifyinghowtogetthosedata.

31.WhatisDMLCompilerIttranslatesDMLstatementsinaquerylanguageintolow-levelinstructionthatthequeryevaluationenginecanunderstand.

32.WhatisQueryevaluationengineItexecuteslow-levelinstructiongeneratedbycompiler.

33.WhatisDDLInterpreterItinterpretsDDLstatementsandrecordthemintablescontainingmetadata.

34.WhatisRecord-at-a-timeTheLowlevelorProceduralDMLcanspecifyandretrieveeachrecordfromasetofrecords.ThisretrieveofarecordissaidtobeRecord-at-a-time.

35.WhatisSet-at-a-timeorSet-orientedTheHighlevelorNon-proceduralDMLcanspecifyandretrievemanyrecordsinasingleDMLstatement.ThisretrieveofarecordissaidtobeSet-at-a-timeorSet-oriented.

36.WhatisRelationalAlgebraItisproceduralquerylanguage.Itconsistsofasetofoperationsthattakeoneortworelationsasinputandproduceanewrelation.

37.WhatisRelationalCalculusItisanappliedpredicatecalculusspecificallytailoredforrelationaldatabasesproposedbyE.F.Codd.E.g.oflanguagesbasedonitareDSLALPHA,QUEL.

38.HowdoesTuple-orientedrelationalcalculusdifferfromdomain-orientedrelationalcalculusThetuple-orientedcalculususesatuplevariablesi.e.,variablewhoseonlypermittedvaluesaretuplesofthatrelation.E.g.QUEL

Thedomain-orientedcalculushasdomainvariablesi.e.,variablesthatrangeovertheunderlyingdomainsinsteadofoverrelation.E.g.ILL,DEDUCE.

39.WhatisnormalizationItisaprocessofanalysingthegivenrelationschemasbasedontheirFunctionalDependencies（FDs）andprimarykeytoachievetheproperties

MinimizingredundancyMinimizinginsertion,deletionandupdateanomalies.

40.WhatisFunctionalDependencyAFunctionaldependencyisdenotedbyXYbetweentwosetsofattributesXandYthataresubsetsofRspecifiesaconstraintonthepossibletuplethatcanformarelationstaterofR.Theconstraintisforanytwotuplest1andt2inrift1[X]=t2[X]thentheyhavet1[Y]=t2[Y].ThismeansthevalueofXcomponentofatupleuniquelydeterminesthevalueofcomponentY.

41.WhenisafunctionaldependencyFsaidtobeminimalEverydependencyinFhasasingleattributeforitsrighthandside.WecannotreplaceanydependencyXAinFwithadependencyYAwhereYisapropersubsetofXandstillhaveasetofdependencythatisequivalenttoF.WecannotremoveanydependencyfromFandstillhavesetofdependencythatisequivalenttoF.

42.WhatisMultivalueddependencyMultivalueddependencydenotedbyXYspecifiedonrelationschemaR,whereXandYarebothsubsetsofR,specifiesthefollowingconstraintonanyrelationrofR:

iftwotuplest1andt2existinrsuchthatt1[X]=t2[X]thent3andt4shouldalsoexistinrwiththefollowingproperties

t3[x]=t4[X]=t1[X]=t2[X]t3[Y]=t1[Y]andt4[Y]=t2[Y]t3[Z]=t2[Z]andt4[Z]=t1[Z]where[Z=（R-（XUY））]

43.WhatisLossles