计算机专业英语的第四版课后习题翻译讲课教案

中译英参考答案

Unit1

Acomputersystemconsistsofhardwaresystemandsoftwaresystem.Thehardwareofthecomputerisusually

dividedintothreemajorpartsorthreeprimarysubsystems:theCPU,thememorysubsystem,andtheI/O

subsystem.

TheCPUperformsmanyoperationsandcontrolscomputer.Thememorysubsystemisusedtostoreprogram

beingexecutedbytheCPU,alongwiththeprogram’sdata.TheI/OsubsystemallowstheCPUtointeractwith

inputandoutputdevicessuchasthekeyboardandmonitorofapersonalcomputer.Thecomponentsofthe

computerareconnectedtothebuses.

Thepartofthecomputerthatperformsthebulkofdataprocessingoperationsiscalledthecentralprocessingunit

andisreferredtoastheCPU.Inmicrocomputer,itisoftencalledthemicroprocessor.TheCPUismadeupof

threemajorparts:controlunit,ALU,andregisterset.

Memoryisalsoknownasinternalmemoryormainmemory.Itreferstothecircuitsinthecomputerthathold

whateverprogramsanddataareavailableforimmediateusebytheCPU.

I/OsubsystemincludesI/Odevicesandinterface.ThereareawidevarietyofI/Odevices,suchasmouse,printer,

sensor,disk,andsoon.Input-outputinterfaceprovidesamethodfortransferringinformationbetweeninternal

storageandexternalI/Odevices.Peripheralsconnectedtoacomputerneedspecialcommunicationlinksfor

interfacingthemwiththeCPU.Thepurposeofthecommunicationlinkistoresolvethedifferencesthatexist

betweenthecentralcomputerandeachperipheral.

Unit2

Storagehardwareprovidespermanentstorageofinformationandprogramsforretrievalbythecomputer.Hard

diskdrivesstoreinformationinmagneticparticlesembeddedinadisk.Usuallyapermanentpartofthecomputer,

harddiskdrivescanstorelargeamountsofinformationandretrievethatinformationveryquickly.

Althoughfixedharddrivesystemsofferfasteraccessandhaveahigherstoragecapacitythanopticaldiscs,

opticaldiscsystemsuseremovablemedia–adistinctbenefit.Opticaldiscs–primaryCDsandDVDs–aremuch

morewidelyusedthanremovableharddrivesystems.Theyarethestandardtodayforsoftwaredelivery,aswell

ascommonlyusedforstoringhigh-capacitymusicandvideofiles.TherearealsoversionsofbothCDandDVD

drivesavailableforhomeaudioandhometheateruse.Opticaldiscsarecommonlyreferredtoascompactdiscs.

CDandDVDdiscsarereadbyCDandDVDdrives.ThespeedofaCDorDVDdriveisratedas24x,32x,36x,

andsoon.Theselabelsdescribehowfastthedriveiscomparedtothefirstversionofthatdrive.Forexample,a

36xdriveis36timesthespeedofthebaselineunitthatwasoriginallymanufactured.Mostopticaldiscshavea

titleandothertextprintedonlyononesideandtheyareinsertedintothedrivewiththeprintedsidefacingup.

WheninsertingsuchaCDorDVD,becarefulnottogetdirt,fingerprints,scratches,oranythingelsethatmight

hinderlightreflectivityonthedisc’ssurface.

Unit3

(a)Aprogramisalistofinstructionsorstatementsfordirectingthecomputertoperformarequireddata

processingtask.Programmingisamultistepprocessforcreatingthatlistofinstructions.

(b)Itisimportanttounderstandthedifferencebetweenaclassandanobjectofthatclass.Aclassissimplya

specificationforcreatingobjects.Thus,asingleclassmaycreatemultipleobjects.

(c)Javaisanobject-oriented,network-friendlyhigh-leverprogramminglanguagethatallowsprogrammersto

buildapplicationsthatcanrunonalmostanyoperatingsystem.

(d)ActiveXisasetofcontrols,orreusablecomponentsthatenablesprogramsorcontentofalmostanytypeto

beembeddedwithinaWebpage.WhereasaJavamustbedownloadedeachtimeyouvisitaWebsite,with

ActiveXthecomponentisdownloadedonlyonce,thenstoredonyourharddiskforlater,repeateduse.

(e)Programminginvolvesagreatdealofcreativity.Thedesignisguidetothefunctionorpurposeofeach

component,buttheprogrammerhasgreatflexibilityinimplementingthedesignascode.Nomatterwhat

languageisused,eachprogramcomponentinvolvesatleastthreemajoraspects:controlstructures,algorithms,

anddatastructures.

Unit4

Thesoftwaresystemcanbedividedintotwobroadcategories:applicationsoftwareandsystemsoftware.

Applicationsoftwareconsistsoftheprogramforperformingtasksparticulartothemachine’sutilization.In

contrasttoapplicationsoftware,systemsoftwarecomprisesalargenumberofprograms.Theseprogramsstartup

thecomputerandfunctionastheprinciplecoordinatorofallhardwarecomponentsandapplicationsoftware.

WithoutsystemsoftwareloadedintoRAMofyourcomputer,yourhardwareandapplicationsoftwareare

useless.

Systemsoftwarecanbegroupedintothreebasicparts:operatingsystem,utilitysoftware,andlanguage

translators.Themajorityofaninstallation’sutilitysoftwareconsistsofprogramsforperformingactivitiesthat

arefundamentaltocomputerinstallationsyetnotincludedintheoperatingsystem.Inasense,utilitysoftware

consistsofsoftwareunitsthatextendthecapabilitiesoftheoperatingsystem.

Acomputer’sOSisthemaincollectionofprogramsthatmanageitsactivities.TheprimarychoresofanOSare

managementandcontrol.TheOSensuresthatallactionsrequestedbyauserarevalidandprocessedinan

orderlyfashion.Italsomanagesthecomputersystem’sresourcestoperformtheseoperationswithefficiencyand

consistency.

Applicationsoftwareisthesoftwaredesignedtohelpyousolveproblemsspecifictobusinessorperformspecific

businesstasks.Applicationsoftwarethenisthelayerofsoftwareclosesttoyou.Basically,therearefour

categoriesofapplicationsoftware:productivitysoftware,businessandspecialtysoftware,entertainmentsoftware

andeducation/referencesoftware.

Unit5

Acomputernetworkisoftenclassifiedasbeingeitheralocalareanetwork(LAN),ametropolitanareanetwork

(WAN),orawideareanetwork(WAN).Theconnectionoftwoormorenetworksiscalledaninternetwork.The

worldwideInternetisawell-knownexampleofaninternetwork.

LANsareprivatelyownednetworkswithinasinglebuildingorcampusofuptoafewkilometersinsize.They

arewidelyusedtoconnectpersonalcomputersandworkstationsincompanyofficesandfactoriestoshare

resourcesandexchangeinformation.

Ingeneral,agivenLANwilluseonlyonetypeoftransmissionmedium.Varioustopologiesarepossiblefor

LANs.ThemostcommonLANtopologiesarebus,ringandstar.

AMANisbasicallyabiggerversionofaLANandnormallyusessimilartechnology.MANisdesignedtoextend

overanentirecity.Itmaybeasinglenetworksuchasacabletelevisionnetwork,oritmaybeameansof

connectinganumberofLANsintoalargenetworksothatresourcesmaybesharedLAN-to-LANaswellas

device-to-device.Forexample,acompanycanuseaMANtoconnecttheLANsinallofitsofficesthroughouta

city.

AWANspansalargegeographicalareathatmaycompriseacountry,acontinent,oreventheworld.Itprovides

long-distancetransmissionofdata,voice,image,andvideoinformationoverlargegeographicalarea.

IncontrasttoLANs,WANsmayutilizepublicleased,orprivatecommunicationdevices,usuallyin

combinations,andcanthereforespananunlimitednumberofmiles.

Unit6

Transmissionmediaareusedtotransfermessagesoveranetwork.Forinstance,thetransmissionmediausedina

networkmaybeaprivatelyownedsetofcables,thepublicphonelines,orasatellitesystem.Transmissionmedia

caneitherbewiredorwireless.

Thethreetypesofwiredmediamostcommonlyusedtocarrymessagesaretwisted-pairwire,coaxialcable,and

fiber-opticcable.Oneofthemostsuccessfuldevelopmentsintransmissionmediainrecentyearshasbeenfiber

optics.Fiber-opticcableiscommonlyusedforthehigh-speedbackbonelinesofanetwork,orforInternet

infrastructure.

Wirelesstransmissionmediahavebecomeespeciallypopularinrecentyears.Theysupportcommunicationsin

situationsinwhichphysicalwiringisimpracticalorinconvenient,aswellasfacilitatemobility.Wirelessmedia

arecommonlyusedtoconnectdevicestoanetwork,toshareinformationbetweencomputers,toconnectwireless

micetoacomputer,andforhandheldPCs,wirelessphones,andothermobiledevices.Radiosignalstransferred

throughtheairaretheheartofmosttypesofwirelessmedia.Inadditiontoconventionalbroadcastradio

application,themicrowave,cellular,andsatellitetransmissionmediaalsouseradiosignalstotransmitdata.

Radiotransmissionsrequiretheuseofatransmittertosendtheradiosignalsthroughtheair.Areceiver(usually

containingsometypeofantenna)acceptsthedateattheotherend.Whenadevicefunctionsasbothareceiver

andtransmitter,itiscommonlycalledatransceiverortransmitter-receiver.

Unit7

(a)Sincemanydatabasesystemsusersarenotcomputertrained,developershidethecomplexityfromusers

throughseverallevelsofabstraction,tosimplifyuser’sinteractionswiththesystem:physicallevel,logicallevel,

andviewlevel.

(b)Adatabaseschemaisspecifiedbyasetofdefinitionsexpressedbyaspeciallanguagecalledadata-definition

language(DDL).TheresultofcompilationofDDLstatementsisasetoftablesthatisstoredinaspecialfile

calleddatadictionary,ordatadirectory.

(c)Thestructuredquerylanguage(SQL)isthemostwidelyusedandstandardquerylanguageforrelational

databasemanagementsystems.Itisakindofnon-procedurallanguage.

(d)Anentityisa“thing”or“object”intherealworldthatisdistinguishablefromotherobjects.Forexample,

eachpersonisanentity,andbankaccountscanbeconsideredtobeentities.Entitiesaredescribedinadatabase

byasetofattributes.

(e)DatawarehouseisoneofthenewestandhottestbuzzwordsandconceptsintheITfieldandthebusiness

environment.Adatawarehouseisalogicalcollectionofinformation——gatheredfrommanydifferent

operationaldatabases——thatsupportsbusinessanalysisactivitiesanddecision-makingtasks.

Unit8

Animationisthetermusedtodescribeaseriesofgraphicalimagesthataredisplayedoneaftertheotherto

simulatemovement.Cartoonsontelevisionareoneexampleofanimation.

Videodiffersfromanimationinthatitusuallybeginsasacontinuousstreamofvisualinformationthatisbroken

intoseparateimagesorframeswhenthevideoisrecorded.Whentheframesareprojected—typicallyatarateof

30framespersecond—theeffectisasmoothreconstructionoftheoriginalcontinuousstreamofinformation.As

youmightimagine,at30framespersecond,theamountofdatainvolvedindisplayingavideoduringa

multimediapresentationcanrequireasubstantialamountofstoragespace.Consequently,videodata—likeaudio

data—isoftencompressed.Avarietyofcompressionstandardsexist.Someofthemostcommonvideofile

formatsare.avi,.mpeg,.mov,.rm.

Formultimediapresentation,videomayberecordedusingastandard(analog)videocameraandthenconverted

todigitalformasitisinputintoacomputer.Alternatively,thefilmcanberecordingdigitallyusingadigital

videocamera.StreamingvideoisfrequentlyusedonWebpagestoreducefilesize.Similartostreamingaudio,

Streamingvideofilescanbeginplayingonceaportionofthevideohasbeendownloaded.

Unit9

(a)AIiscurrentlybeingappliedinbusinessintheformofknowledgesystems,whichusehumanknowledgeto

solveproblems.Themostpopulartypeofknowledge-basedsystemistheexpertsystem.Anexpertsystemisa

computerprogramthatattemptstorepresenttheknowledgeofhumanexpertsintheformofheuristics.Theterm

heuristicisderivedfromthesameGreekrootasthewordeureka,whichmeans“todiscover”.

(b)Theuserinterfaceenablesthemanagertoenterinstructionsandinformationintotheexpertsystemandto

receiveinformationfromit.Theinstructionsspecifytheparametersthatguidetheexpertsystemthroughits

reasoningprocessing.Theinformationisintheformofvaluesassignedtocertainvariables.

(c)Theknowledgebasecontainsbothfactsthatdescribetheproblemareaandknowledgerepresentation

techniquesthatdescribehowthefactsfittogetherinalogicalmanner.Thetermproblemdomainisusedto

describetheproblemarea.

(d)Anexpertsystem,alsocalledaknowledge-basedsystem,isanartificialintelligencesystemthatapplies

reasoningcapabilitiestoreachaconclusion.Expertsystemsareexcellentfordiagnosticandprescriptive

problems.

(e)TheDSSisnotintendedtoreplacethemanager.Thecomputercanbeappliedtothestructuredportionofthe

problem,butthemanagerisresponsiblefortheunstructuredportion——applyingjudgmentorintuitionand

conductinganalyses.

Unit10

Thelinkedlist(seefigure1)consistsofaseriesofnodes,whicharenotnecessarilyadjacentinmemory.Each

nodecontainstheelementandalinktoanodecontainingitssuccessor.Wecallthisthenextlink.Thelastcell’s

nextlinkreferencesnull.

ToexecuteprintListorfind(x)wemerelystartatthefirstnodeinthelistandthentraversethelistbyfollowing

thenextlinks.Thisoperationisclearlylinear-time,asinthearrayimplementation,althoughtheconstantislikely

tobelargerthanifanarrayimplementationwereused.ThefindKthoperationisnolongerquiteasefficientasan

arrayimplementation;findKth(i)takesO(i)timeandworksbytraversingdownthelistintheobviousmanner.In

practice,thisboundispessimistic,becausefrequentlythecallstofindKthareinsortedorder(byi).Asan

example,findKth(2),findKth(3),findKth(4),andfindKth(6)canallbeexecutedinonescandownthelist.

Theremovemethodcanbeexecutedinonenextreferencechange.Figure2showstheresultofdeletingthe

secondelementintheoriginallist.

Theinsertmethodrequiresobtaininganewnodefromthesystembyusinganewcallandthenexecutingtwo

referencemaneuvers.Thegeneralideaisshowninfigure3.Thedashedlinerepresentstheoldnextreference.

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Unit11

(a)Asetispureifallofitsmembersaresets,allmembersofitsmembersaresets,andsoon.Forexample,the

setcontainingonlytheemptysetisanonemptypureset.

(b)Alanguageisadescribablesetoffinitestrings,drawnfromafixedalphabet.Agrammarisonewayto

"describe"thelanguage.Thegrammarconsistsofafinitelistofrules,whereeachrulereplacesonesubstring

withanother.Thestringontheleftmustcontainatleastonenonterminal.Thefirststring"produces"or

"generates"thesecond.Thusaruleisalsocalledaproduction.

(c)Afinite-statemachine(FSM)orfinite-stateautomaton（FA）isamathematicalabstractionsometimesused

todesigndigitallogicorcomputerprograms.Itisabehaviormodelcomposedofafinitenumberofstates,

transitionsbetweenthosestates,andactions,similartoaflowgraphinwhichonecaninspectthewaylogicruns

whencertainconditionsaremet.

(d)Sometimesitisinconvenientorimpossibletodescribeasetbylistingallofitselements.Anotherusefulway

todefineasetisbyspecifyingapropertythattheelementsofthesethaveincommon.ThenotationP(x)isused

todenoteasentenceorstatementPconcerningthevariableobjectx.ThesetdefinedbyP(x)written{x|P(x)},is

justacollectionofalltheobjectsforwhichPistrue.

Unit12

(a)Becausedrawingsaretypicallydisplayedin3D,CADisespeciallyhelpfulindesigningautomobiles,aircraft,

ships,buildings,electricalcircuits(includingcomputerchips),andevenclothing.

(b)Computer-integratedmanufacturing(CIM)isthemanufacturingapproachofusingcomputerstocontrolthe

entireproductionprocess.Thisintegrationallowsindividualprocessestoexchangeinformationwitheachother

andinitiateactions.Throughtheintegrationofcomputers,manufacturingcanbefasterandlesserror-prone,

althoughthemainadvantageistheabilitytocreateautomatedmanufacturingprocesses.

(c)Inadditiontosupportingdecisionmaking,coordination,andcontrol,informationsystemmayalsohelp

managersandworkersanalyzeproblems,visualizecomplexsubjects,andcreatenewproducts.

(d)KnowingthehistoryandevolutionofERPisessentialtounderstandingitscurrentapplicationanditsfuture

developments.

(e)Inadditiontomonitoringoperationalactivitiessuchastrackingthestatusofordersandinventorylevels,

enterprisesystemalsoimproveorganization-widereportinganddecisionmaking.

Unit13

(a)Thereareawidevarietyofeducationalapplicationprogramsavailable.Educationalsoftwareisdesignedto

teachoneormoreskills,suchasreading,math,spelling,aforeignlanguage,worldgeography,ortohelpprepare

forstandardizedtests.

(b)Electronicbusiness(e-business)istheuseofinformationtechnologyandelectroniccommunicationnetworks

toexchangebusinessinformationandconducttransactionsinelectronic,paperlessform.

(c)Wordprocessingsoftwareallowsyoutousecomputerstocreate,edit,store,andprintdocuments.Youcan

easilyinsert,delete,andmovewords,sentences,andparagraphs——withouteverusinganeraser.

(d)Whatisaspreadsheet?Spreadsheetsoftwaretakesitsnamefromtheaccountant’scolumnarworksheet,which

itimitates.Aspreadsheetisaworksheetconsistingofacollectionofcellsformedbytheintersectionofrowsand

columns.Eachcellcanstoreonepieceofinformation:anumber,wordorphrase,orformula.

Unit14

(a)Ageographicinformationsystem(GIS)isasystemthatcaptures,stores,analyzes,managesandpresentsdata

withreferencetogeographiclocationdata.Inthesimplestterms,GISisthemergingofcartography,statistical

analysisanddatabasetechnology.

(b)TheGPSreceiverusesthemessagesitreceivestodeterminethetransittimeofeachmessageandcomputes

thedistancetoeachsatellite.Thesedistancesalongwiththesatellites'locationsareusedtocomputetheposition

ofthereceiver.Thispositionisthendisplayed,perhapswithamovingmapdisplayorlatitudeandlongitude;

elevationinformationmaybeincluded.

(c)Virtualreality(VR)isatermthatappliestocomputer-simulatedenvironmentsthatcansimulatephysical

presenceintherealworld.Mostcurrentvirtualrealityenvironmentsareprimarilyvisualexperiences,displayed

eitheronacomputerscreenorthroughspecialstereoscopicdisplays,butsomesimulationsincludeadditional

sensoryinformation,suchassoundthroughspeakersorheadphones.

Unit15

(a)Thesoftwaredevelopmentprocessissometimescalledthesoftwaredevelopmentlifecycle(SDLC),because

itdescribesthelifeofasoftwareproductfromitsconceptiontoitsimplementation,delivery,use,and

maintenance.

(b)HowcantheCMMhelpyourorganization?TherearethreekeyrolestheCMMplays.First,theCMMhelps

buildanunderstandingofsoftwareprocessbydescribingthepracticesthatcontributetoalevelofprocess

maturity.ThesecondroleoftheCMMistoprovideaconsistentbasisforconductingappraisalsofsoftware

processes.TheCMM’sthirdkeyroleistoserveasablueprintforsoftwareprocessimprovement.

(c)TheUMLoffersastandardwaytowriteasystem’sblueprints,includingconceptualthingssuchasbusiness

processesandsystemfunctionsaswellasconcretethingssuchasprogramminglanguagestatements,database

schemas,andreusablesoftwarecomponents.TheUMLrepresentsacollectionofthebestengineeringpractices

thathaveprovensuccessfulinthemodelingoflargeandcomplexsystems.

(d)Objectmodelingisatechniqueforidentifyingobjectswithinthesystemenvironmentandtherelationships

betweenthoseobjects.Theobject-orientedapproachtosystemdevelopmentisbasedonseveralconcepts,suchas

object,attribute,behavior,encapsulation,class,inheritance,polymorphism,persistence,etc.

Unit16

“Security”isanall-encompassingtermthatdescribesalltheconcepts,techniques,andtechnologiestoprotect

informationfromunauthorizedaccess.Thereareseveralrequirementsforinformationsecurity.

Confidentiality:hidingdata,usuallywithencryption,topreventunauthorizedviewingandaccess.

Authenticity:theabilitytoknowthatthepersonorsystemyouarecommunicatin