《计算机专业英语》-Unit6Database

TextA:EntertheWorldofRelationalDatabase下一页返回TextA:EntertheWorldofRelationalDatabaseIntoday’sbusinessworld,informationtechnologyisinitsfullboom.Processingdataandpumpingoutinformationhasbecomethefocalpointofthemoderndaycomputingenvironment.Datacanbestoredinvariousways,dependingonhowitwillbeusedlateron.Thisdatastoreiscalledadatabase.Therawestformofdatastorageisafilewheredataisstoredwithoutanyattributes,characteristicsorlinks.Itrequiresalotofprogrammingefforttoprocessthistypeofdata,sotherelationaldatamodelevolved.Therelationaldatamodelrepresentsdataandrelationshipsamongthedataelements.Thismodelisbasedonrealworldscenarios,whichconsistofbasicobjectsknownasentitiesandhowtheseentitiesareconnectedwitheachother,whichconstitutestherelationships.ApresentationofthisconceptisknownasanERD上一页下一页返回TextA:EntertheWorldofRelationalDatabase(entityrelationshipdiagram).Let’stakeasimpleexampleofadatabaseforabookstore.Booktitlesandauthorsaretwoentitiesinit(amongmanyothers).Therelationshipbetweenauthorsandbooksisthatmanyauthorscanwriteonebookandoneauthorcanhaveseveralbooks.Thistypeofrelationshipiscalledan“anytomany”relationship.SchematicrepresentationsoftheserelationshipsareshowninFigure5-1.

上一页下一页返回TextA:EntertheWorldofRelationalDatabaseToidentifyalltheentitiesandtheirrelationshipsisthefirststepofrelationaldatamodeling.Thisisalsoknownas“logicaldatabasedesign.”Oncethelogicaldesigniscompleted,itrequirescreatingsomekindsofphysicalobjects(knownas“table”)tostorethisinformation.Weshouldneedasystemthatwouldfacilitatestoringentitieswiththeirattributesandrelationships.Thissystemshouldalsoprovidethecapabilityofretrievingthedesiredinformationabouttheentities.上一页下一页返回TextA:EntertheWorldofRelationalDatabaseⅡ.IntroductiontoaDatabaseManagementSystemAdatabasemanagementsystemisacomputerbasedsystemtorecordinterrelateddata,anditprovidesinterfacestoaccessthedata.Adatabasesystemisdesignedtohandlealargeamountofdataandisbothconvenientandefficienttouse.Theoverallpurposeofadatabasesystemistomaintaininformationinsuchawaythat:DataredundancyisreducedDataintegrityismaintainedDataaccessiseasyDataissecuredDatasharingispossible上一页下一页返回TextA:EntertheWorldofRelationalDatabaseWordsandExpressionsanomaly:n.异常（现象）associate:v.联系，联合attribute:n.属性characteristic:adj.典型的，独特的concurrent:adj.同时发生，并发的constitute:v.组成，构成diagram:n.图示，图解duplication:n.重复，复制entity:n.实体上一页下一页返回TextA:EntertheWorldofRelationalDatabasefacilitate:v.使更容易focal：adj.焦点的

inconsistency:n.不一致interface:n.界面interrelate:v.使相互关联rawest:adj.最原始的redundancy:n.冗余relational:adj.有关系的，相关的relationship:n.联系representation:n.体现，表示retrieve:v.恢复，重获上一页下一页返回TextA:EntertheWorldofRelationalDatabasescenario:n.方案，设想pumpingout:提取，抽取viceversa:反之亦然computerbased:基于计算机的dueto:因为，由于上一页下一页返回TextA:EntertheWorldofRelationalDatabaseNotes

①Thismodelisbasedonrealworldscenarios,whichconsistofbasicobjectsknownasentitieshowtheseentitiesareconnectedwitheachother,whichconstitutestherelationships.

这种模型基于现实世界的情况，包括被称为实体的基本对象以及构成这些实体间关系的互联方式。②Adatabasemanagementsystemisacomputerbasedsystemtorecordinterrelateddata,anditprovidesinterfacestoaccessthedata.

数据库管理系统是记录相互关联数据的基于计算机的系统，它为访问数据提供界面。上一页下一页返回TextA:EntertheWorldofRelationalDatabase③Dataduplicationisminimizedasmuchaspossible,whichisanefficientstoragestrategythateliminatesdatainconsistencies.

数据重复应尽可能地减少，这是消除数据不一致的有效存储策略。④Thedatainaccuracycanbeduetoinconsistencies(asdiscussedpreviously)orduetonotfollowingsomevalidconstraints—e.g.,30thdayofFebruaryisaninaccuratedatavalue.⑤ADBMScansupportmultipleusersandnoteveryusershouldbeabletoaccessallthedata.

数据库管理系统支持多用户，但也不意味着每个用户可以接触数据库里的所有数据。上一页返回TextB:DatabaseManagementSystemsThetermdatabaseisoftentodescribeacollectionofrelatedfilesthatisorganizedintoanintegratedstructurethatprovidesdifferentpeoplevariedaccesstothesamedata.Inmanycasesthisresourceislocatedindifferentfilesindifferentdepartmentsthroughoutthisorganization,oftenknownonlytotheindividualswhoworkwiththeirspecificportionofthetotalinformation.Inthesecases,thepotentialvalueoftheinformationgoesunrealizedbecauseapersoninotherdepartmentswhomayneeditdoesnotknowitoritcannotbeaccessedefficiently.Inanattempttoorganizetheirinformationresourcesandprovidefortimelyandefficientaccess,manycompanieshaveimplementeddatabases.下一页返回TextB:DatabaseManagementSystems上一页下一页返回TextB:DatabaseManagementSystemsAdatabaseisacollectionofrelateddata.Bydata,wemeanknownfactsthatcanberecordedandthathaveimplicitmeaning.Forexample,thenames,telephonenumbers,andaddressesofallthepeopleyouknow.Youmayhaverecordedthesedatainanindexedaddressbook,oryoumayhavestoredthemonadisketteusingapersonalcomputerandsoftwaresuchasDBASEIIIorLotus1-2-3.Thisisacollectionofrelateddatawithanimplicitmeaningandhenceisadatabase.Theabovedefinitionofdatabaseisquitegeneral.Forexample,wemayconsiderthecollectionofwordsthatmakeupthispageoftexttoberelateddataandhenceadatabase.However,thecommonuseofthetermdatabaseisusuallymorerestricted.Adatabasehasthefollowingimplicitproperties:上一页下一页返回TextB:DatabaseManagementSystemsAdatabaseisalogicallycoherentcollectionofdatawithsomeinherentmeaning.Arandomassortmentofdatacannotbereferredtoasadatabase.Adatabaseisdesigned,built,andpopulatedwithdataforaspecificpurpose.Ithasanintendedgroupofusersandsomepreconceivedapplicationsinwhichtheseusersareinterested.Adatabaserepresentssomeaspectsoftherealworld,sometimescalledthemini-world.Changestotheminiworldarereflectedinthedatabase.Inotherworld,adatabasehassomesourcesfromwhichdataarederived,somedegreeofinteractionwitheventsintherealworld,andanaudiencewhoisactivelyinterestedinthecontentsofthedatabase.上一页下一页返回TextB:DatabaseManagementSystems1.DatabaseManagementSystemThesemultiuserdatabasesaremanagedbyapieceofsoftwarecalledaDatabaseManagementSystem(DBMS).Itisthiswhichdifferentiatesadatabasefromanordinarycomputerfile.Betweenthephysicaldatabaseitself(i.e.thedataasactuallystored)andtheusersofsystemistheDBMS.Allrequestsforaccesstodatafromusers—whetherpeopleatterminalsorotherprogramsrunninginbatch—arehandledbytheDBMS.OnegeneralfunctionoftheDBMSistheshieldingofdatabaseusersfrommachinecode.Inotherwords,theDBMSprovidesaviewofthedatathatiselevatedabovethehardwarelevel,andsupportsuserrequestssuchas“GetthePATIENTrecordforpatientSmith,”writteninahigherlevellanguage.上一页下一页返回TextB:DatabaseManagementSystemsTheDBMSalsodeterminestheamountandtypeofinformationthateachusercanaccessfromadatabase.Forexample,asurgeonandahospitaladministratorwillrequiredifferentviewsofadatabase.Whenauserwishestoaccessadatabase,hemakesanaccessrequestusingaparticulardatamanipulationlanguageunderstoodbytheDBMS.TheDBMSreceivestherequest,andchecksitforsyntaxerrors.TheDBMStheninspects,inturn,theexternalschema,theconceptualschema,andthemappingbetweentheconceptualschemaandtheinternalschema.Itthenperformsthenecessaryoperationsonthestoreddata.上一页下一页返回TextB:DatabaseManagementSystems2.LogicalStructuresofDBMS(1)ListstructuresInthislogicalapproach,recordsarelinkedtogetherbytheuseofpoints.Apointerisadataiteminonerecordthatidentifiesthestoragelocationofanotherlogicallyrelatedrecord.Recordsinacustomermasterfile,forexample,willcontainthenameandaddressofeachcustomerandeachrecordinthisfileisidentifiedbyanaccountnumber.Duringanaccountingperiod,acustomermaybuyanumberofitemsondifferentdays.Thus,thecompanymaymaintainaninvoicefiletoreflectthesetransactions.Aliststructurecouldbeusedinthissituationtoshowtheunpaidinvoicesatanygiventime.上一页下一页返回TextB:DatabaseManagementSystems(2)TreestructuresInthislogicalapproach,dataunitsarestructuredinmultiplelevelsthatgraphicallyresemblean“upsidedown”treewiththerootatthetopandthebranchesformedbelow.Thereisasuperiorsubordinaterelationshipinatreestructure.Belowthesinglerootdatacomponentaresubordinateelementsornodes,eachofwhich,inturn,“owns”oneormoreotherelements(ornone).上一页下一页返回TextB:DatabaseManagementSystems(3)NetworkstructuresUnlikethetreeapproach,whichdoesnotpermittheconnectionofbranches,thenetworkstructurepermitstheconnectionofthenodesinamultidirectionalmanner.Thus,eachnodemayhaveseveralownersandmay,inturn,ownanynumberofotherdataunits.Datamanagementsoftwarepermitstheextractionoftheneededinformationfromsuchastructurebybeginningwithanyrecordinafile.上一页下一页返回TextB:DatabaseManagementSystems(4)RelationalstructuresArelationalstructureismadeupofmanytables.Thedataarestoredintheformof“relation”inthesetables.Forexample,relationtablescouldbeestablishedtolinkacollegecoursewiththeinstructorofthecourse,andwiththelocationoftheclass.3.InformationSystemTheobjectiveofinformationsystemistoprovideinformationtoalllevelsofmanagementatthemostrelevanttime,atanacceptablelevelofaccuracy,andataneconomicalcost.上一页下一页返回TextB:DatabaseManagementSystemsIndividualbusinessrequiresinformationaccordingtothenatureoftheiroperations.Acarmanufacturerisparticularlyinterestedintheextentofcompetitionfromoverseasmanufacturersinthehomemarketandcompetitionfromotherhomebasedmanufacturers.Atouroperatorisconcernedaboutpurchasingpoweranditseffectonholidaybookingsandpoliticalsituationprevailinginthevariouscountries.Asageneralguide,thedetailcontainedinreportscontaininginformationvariesaccordingtothepositionoftherecipientinthehierarchicalmanagementstructure.Theyrequireinformationrelatingtoeventsastheyoccursothatappropriateactioncanbetakentocontrolthem.上一页下一页返回TextB:DatabaseManagementSystemsWordsandExpressionsappropriate:adj.适当的assortment:n.分类,各种各样audience:n.观众coherent:adj.一致的，连贯的differentiate:v.区别，区分elevate:v.举起，提拔上一页下一页返回TextB:DatabaseManagementSystemsextraction:n.抽取，取出formidable:adj.艰难的，令人敬畏的

implicit:adj.暗示的，固有的interaction:n.交互作用invoice:n.发票preconceive:v.事先认为prevailing:adj.优势的，主要的purchase:v.购买reflect:v.反映上一页下一页返回TextB:DatabaseManagementSystemsresemble:v.相似，类似restrict:v.限制，限定schema:n.模式shielding:n.屏蔽，防护层surgeon:n.外科医生transaction:n.事务上一页下一页返回TextB:DatabaseManagementSystemsNotes①Adatabaseisdesigned,bulit,andpopulatedwithdataforaspecificpurpose.②Eachlogicalrecordoccurrencemay,inturn,requiredatafrommorethanonephysicalrecordheldintheactualdatabase.③Asageneralguide,thedetailcontainedinreportscontaininginformationvariesaccordingtothepositionoftherecipientinthehierarchicalmanagementstructure.④Theyrequireinformationrelatingtoeventsastheyoccursothatappropriateactioncanbetakentocontrolthem.

上一页返回GrammarFocus一、主语+系动词+表语（SVC）众所周知英文的谓语动词分两大类：一类是系动词；另一类是实义动词。由于动词在谓语的构成方面要求不一样，就有了5种英文基本句型。其中，由实义动词构成的谓语有4种，由系动词构成的谓语却仅有一种。

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系动词后接的部分可称为表语；也可称为（主语）补足语，因为这一部分的主要功能是对主语进行说明、补充。这种结构与中文里的“判定合成谓语”很有相似之处，都是用来说明主语的性质、状态、特征、职业、年龄等。英文中的系动词主要是指Be动词的各种变化形式，也包括那些有时起系动词作用的实义动词。这类动词常见的有：become(变成),look(看上去),seem(看起来)，appear(相似、显得),get(变得)，feel(摸起来)，grow(变得)，turn(变成),remain(仍然是),come(变得),fall(变得