《计算机专业英语》习题.docx
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《计算机专业英语》习题.docx
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《计算机专业英语》习题
计算机专业英语
Passage(A)
CharacteristicsofClientsandServers
Thetermclientandserverrefertothetwoapplicationsinvolvedinacommunication.Theapplicationthatactivelyinitiatescontactiscalledaclient,whiletheapplicationthatpassivelywaitsforcontactiscalledaserver.
Confusionsometimesarisesoverthetermserver.Formally,thetermreferstoaprogramthatwaitspassivelyforcommunication,andnottothecomputeronwhichexecutes.However,whenacomputerisdedicatedtorunningoneormoreserverprograms,thecomputeritselfissometimes(incorrectly)calledaserver.HardwarevenderscontributetotheconfusionbecausetheyclassifycomputersthathavefastCPUs,largememories,andpowerfuloperatingsystemsasservermachines.
Weadheretoscientificallyaccurateterminologyandusethetermservertorefertotherunningprogramandnotthecomputer.Thetermserver-classcomputerreferstoapowerfulcomputerusedtorunserversoftware.
Informationcanpassineitherorbothdirectionsbetweenaclientandaserver.Typically,aclientsendsarequesttoaserver,andtheserverreturnsaresponsetotheclient.Insomecases,aclientsendsaseriesofrequestsandtheserverissuesaseriesofresponses(e.g.,adatabaseclientmightallowausertolookupmorethanoneitematatime).Inothercases,theserverprovidescontinuousoutputwithoutanyrequest--assoonastheclientcontactstheserver,theserverbeginssendingdata(e.g.,alocalweatherservermightsendcontinuousweatherreportWithupdatedtemperatureandbarometricpressure).
Itisimportanttounderstandthatserverscanacceptincominginformationaswellasdeliveroutgoinginformation.Forexample,mostfileserversareconfiguredtoexportasetoffilestoclients,Thatis,aclientsendsarequestthatcontainsafilename,andtheserverresponsesbysendingacopyofthefile.However,afileservercanalsobeconfiguredtoimportfiles(i.e.,toallowaclienttosendacopyofafile,whichtheserveracceptsandstoresondisk).
Althoughminorvariationsexist,mostinstancesofclient-serverinteractionhavethesamegeneralcharacteristics.Ingeneral,clientsoftware:
●isanarbitraryapplicationthatbecomesaclienttemporarilywhenremoteaccessisneeded,butalsoperformsothercomputationlocally.
●isinvokeddirectlybyauser,andexecutesonlyforonesession.
●runslocallyonauser'spersonalcomputer.
●canaccessmultipleservicesasneeded,butactivelycontactsoneremoteserveratatime.
●doesnotrequirespecialhardwareorasophisticatedoperatingsystem.
Incontrast,serversoftware:
●isaspecial-purpose,privilegedprogramdedicatedtoprovidingoneservice,butcanhandlemultipleremoteclientsatthesametime.
●isinvokedautomaticallywhenasystemboots,andcontinuestoexecutethroughmanysessions.
●runsonasharedcomputer(i.e.,notonauser'spersonalcomputer).
●waitspassivelyforcontactfromarbitraryremoteclients.
●acceptscontactfromarbitraryclients,butoffersasingleservice.
●requirespowerfulhardwareandsophisticatedoperatingsystem.
Choosethebestanswerforeachofthefollowing
1.Theclientisregardedasactiveinacommunicationcomparedwiththeserverbecause______
(A)thecommunicationisinitiatedbytheclient
(B)theserverneversendsarequesttotheclient
(C)therequestissentbytheclient
(D)theserveriswaitingforcontactpassively
2.Thereasonwhythevenderscreateconfusiononpurposeastothetermserveris
(A)thattheydon'tknowthecorrectdefinitionofthetermsever
(B)notmentioned
(C)thattheywanttocontrolthecomputermarket
(D)thattheywanttheircomputerstobeusedastheservers
3.Whichofthefollowingisnotthecharacteristicoftheclientsoftware?
(A)Performinglocalcomputation.
(B)Runningonpersonalcomputer.
(C)Accessingoneserviceatatime.
(D)Initiatingthecontactactively.
4.Whichofthefollowingisnotthecharacteristicoftheserversoftware?
(A)Handlingmultipleremoteclientsatthesametime.
(B)Beinginvokedautomaticallybyasystemboot
(C)Executingthroughmanysessions.
(D)Offeringmultipleservices.
5.Whatwillhappenifafileserverisconfiguredonlytodeliveroutgoinginformation?
(A)Itcanonlyexportfilestotheclients.
(B)Itcannotimportanyfilesfromanyclients.
(C)Itcannotstoreanyclient'sfilesonitsharddisk.
(D)Alloftheabove.
WriteT(true)orF(false)foreachstatement
1.Aservercanonlyacceptincominginformation.
2.Powerfulcomputersareservercomputers.
3.Someserversdon'treturnanyresponsebeforeissuinginformationrequestedbytheclient.
4.Thecomputeronwhichtheclientprogramexecutesisnotnecessarilyapowerfulcomputer.
5.Theserversoftwareisinvokedbytheclientapplication.
Passage(B)
IntroductiontoRelationalDatabase
Thefunctionalityofdatabasemanagementandinformationsystemsrestsonawell-establishedtechnology.Thebasisofthistechnologyconsistsofmethodsforstructuringandorganizingdata.Dataneedstobeorganizedifitistobeuseful.Datamodelsspecifyhowseparatepiecesofinformationarerelatedinadatabase.Informationisgenerallybrokendownintodatastructures.Themostbasicofthesestructuresarerecordsandfields.Atfirstlevel,recordsarethebasicunitsofdatastorage.Fields,suchasSocialSecuritynumberandbirth-date,aretheelementarydataitems.Syntactically,theinformationthatafieldcontainsconformstoacertaintypesuchasareal,aninteger,acharacterorastring.Semantically,themeaningofinformationwithinafieldcorrespondstotheconceptorattributerepresentedbythefield.
Therelationaldatabasemodelfollowedonfromhierarchicalandnetworkdatabasesandis
presentlythemostwidelyuseddatamodelfordatabase.Priorto1970,mainframedatabase
applicationsweredominatedbynetworkandhierarchicalmodels.ThenCodd(1970)proposed
therelationaldatamodel.IBMatSanJoesimplementedthefirstworkingversionoftherelationalmodelintheirsystem/R.
Eachrowinarelationrepresentsarelationshipbetweenasetofvalues.Onereasonforthe
widespreadacceptanceoftherelationalmodelmaybethatitisbasedonthisstraightforwardandeasilyunderstoodconceptualmodel.Therelationalmodelcanbesummarizedintermsoftables
andoperationsontablesusingtherelationalalgebra.Arelationaldatabaseconsistsoftables.Eachtablebearsthenameofarelationandcontainsrowsandcolumns.Wecandefinearelationschemeasthesetofattributenamesforarelation.Newtablescanbeconstructedfromthesetablesbycuttingandpastingrowsandcolumnsfromtheexistingtables.Theprocessofconstructingnewtablesintherelationalmodelisgovernedbytheoperationsoftherelational
algebra.
Onceweattachattributenamestothecolumnsofarelationaltable,theorderofthecolumns
(attributes)becomesunimportant.Conceptually,operationsonthisrelationaldatabaseconsistofcuttingandpastingportionsoftheexistingtablestocreatenewrelationaltablesthatsatisfycertaincriteria.Therelationaldatabasemodeloffersthesimplenotionoftablesastheonlydatastructureforuserinteraction.Itscloserelationshiptosettheoryandfirstorderlogicallowstherelationalmodeltoinheritmanyelegantpropertiesandoperatorssinceitisbasedonawell-definedlogicalstructure,namely,therelationalalgebra.
Dataretrievalwithintherelationalmodelishandledbyusingtherelationalalgebrato
manipulaterelations.ThefivefundamentaloperationsintherelationalalgebraareSelection,
Projection,Product,Union,andSetdifference.Inaddition,thejoinisanotheroperationthat
maybedefinedintermsoftheCartesianproductandselectionoperation.
Anumberoflanguagesweredevelopedtoprovideefficientqueryingwithintheframeworkoftherelationalalgebra.TwomajorapproachesarebasedonthelanguagesSQLandQUEL.AnotherinnovativequerylanguagewasknownasQuery-By-Example.
Choosethebestanswerforeachofthefollowing
1.Theinformationcontainedinafieldshouldconformto__________.
(A)themeaningofinformationwithinafield
(B)theconceptorattributerepresentedbythefield
(C)acertaintypeofdata
(D)acertaindatastructure
2.Whatdominatedthemainframedatabaseapplicationsbeforetheestablishmentofrelationaldatabasemodel?
(A)Intelligentdatabase.
(B)Networkandhierarchicaldatabase.
(C)Object-orienteddatabase.
(D)Multimediadatabase.
3.Whycanrelationaldatabasemodelspreadwidely?
(A)Becausethemodelcanbesummarizedintermsoftablesandoperationsontablesusingrelationalalgebra.
(B)Becausetherelationalmodelconsistsofonlytables.
(C)Becausetherelationalmodelcanbeeasilydefinedasasetofattributenames.
(D)Becausethemodelisstraightforwardandeasilyunderstood.
4.Thenewrelationaltablesinarelationaldatabasecanbecreatedby______.
(A)followingtheprincipleoftherelationalalgebra
(B)cuttingandpastingportionsofexistingtables
(C)assigningnewattributenamestotherowsandcolumnsoftheexistingtables
(D)noneoftheabove
5.Thedatawithintherelationaldatabasecanberecovered______.
(A)bycopyingfromthebackupfiles
(B)fromtherelationaltablesofthedatabase
(C)byusingrelationalalgebratomanipulatetherelations
(D)byusingthequerylanguagessuchasSQLorQUEL.
WriteT(true)orF(false)foreachstatement
1.Thehierarchicalandnetworkdatabasesweredevelopedearlierthantherelationaldatabase.
2.Therelationaldatabasemodelwasthedominantdatabasemodelbe
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