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PART1COMPUTERHARDWARECHAPTER2COMPUTEROPERATINGSYSTEM2-4THEMIDDLEWARE2.4THEMIDDLEWAREMainPoint●Whatismiddleware●Functionsandcharacteristicsofmiddleware●DifferencesbetweenoperatingsystemandmiddlewareKEYWORDS:persistentstorage持久储存器middleware中间件ApplicationProgramInterface(API)应用程序接口variable-lengthfile可变长文件relationaldatabase关系型数据库bundle捆，卷，捆绑件hostname主机名Nowthatyouknowwhatanoperatingsystemis,Icanturntotheothercategoryofsoftwarecoveredbythisbook:middleware.[1]Middlewareissoftwareisoccupyingamiddlepositionbetweenapplicationprogramsandoperatingsystems,asIwillexplaininthissection.Operatingsystemsandmiddlewarehavemuchincommon.Botharesoftwareusedtosupportothersoftware,suchastheapplicationprogramsyourun.连接词宾语从句方式状语从句同位语定语从句Bothprovideasimilarrangeofservicescenteredaroundcontrolledinteraction.Likeanoperatingsystem,middlewaremayenforcerulesdesignedtokeepthecomputationsfrominterferingwithoneanother.[2]Anexampleistherulethatonlyonecomputationmaymodifyashareddatastructureatatime.Likeanoperatingsystem,middlewaremaybringcomputationsatdifferenttimesintocontactthroughpersistentstorageandmaysupportinteractionbetweencomputationsondifferentcomputersby宾语补语同位语从句providingnetworkcommunicationservices.[3]Operatingsystemsandmiddlewarearenotthesame,however.Theyrelyupondifferentunderlyingprovidersoflower-levelservices.AnoperatingsystemprovidestheservicesinitsAPIbymakinguseofthefeaturessupportedbythehardware.?1Whichfeaturesarethesamebetweenoperatingsystemandmiddleware?Forexample,itmightprovideAPIservicesofreadingandwritingnamed,variable-lengthfilesbymakinguseofadiskdrive’sabilitytoreadandwritenumbered,fixed-lengthblocksofdata..[4]Middleware,ontheotherhand,providestheservicesinitsAPIbymakinguseofthefeaturessupportedbyanunderlyingoperatingsystem.Forexample,themiddlewaremightprovideAPIservicesforupdatingrelationaldatabasetablesbymakinguseofanoperatingsystem’sabilitytoreadandwritefilesthat定语从句宾语①宾语②宾语③Thislayeringofmiddlewareontopofanoperatingsystem,asillustratedinFigure2-2,explainsthename;middlewareisinthemiddleoftheverticalstack,betweentheapplicationprogramsandtheoperatingsystem.Viewedhorizontallyratherthanvertically,middlewareisalsointhemiddleofinteractions方式状语containthedatabase.?2Whichfeaturesarenotcommonbetweenoperatingsystemandmiddleware?betweendifferentapplicationprograms(possiblyevenrunningondifferentcomputersystems),becauseitprovidesmechanismstosupportcontrolledinteractionthroughcoordination,persistentstorage,naming,andcommunication.原因状语从句ApplicationApplicationMiddlewareOperatingSystemApplicationOperatingSystemMiddlewareDatabaseTableFig2-2middlewareuserservicesfromanoperatingsystemandinturnprovidesservicestoapplicationprogramstosupportcontrolledinteraction.?3WhichappearanceofthingcanweseefromFig.2-2?Ialreadymentionedrelationaldatabasesystemsasoneexampleofmiddleware.Suchsystemsprovideamoresophisticatedformofpersistentstoragethanthefilessupportedbymostoperatingsystems.IuseOracleasmyprimarysourceofexamplesregardingrelationaldatabasesystems.比较结构OthermiddlewareIwilluseforexamplesinthebookincludestheJava2Platform,EnterpriseEdition(J2EE)andIBM’sWebSphereMQ..[5]Thesesystemsprovidesupportforkeepingcomputationslargelyisolatedfromundesirableinteractions,whileallowingthemtocommunicatewithoneanotherevenifrunningondifferentcomputers.Themarketingdefinitionofmiddlewaredoesn’talwayscorrespondexactlywithmytechnicaldefinition.定语从句并列Inparticular,somemiddlewareisofsuchfundamentalimportancethatitisdistributedaspartoftheoperatingsystembundle,ratherthanasaseparatemiddlewareproduct.[6]Asanexample,general-purposeoperatingsystemsallcomeequippedwithsomemechanismfortranslatingInternethostnames,suchas[7]Thesemechanismsaretypicallyoutsidetheoperatingsystemkernel,but表语同位语从句同位语provideageneralsupportingservicetoapplicationprograms.Therefore,bymydefinition,theyaremiddleware,evenifnotnormallylabeledassuch.?4IstheOracleasonemiddleware?条件状语从句NOTES[1]nowthat作连接词用，表示“既然”[2]keep+from使……不能（做某事），阻止，此处是指使计算机任务不受干扰。designed……过去分词短语作宾语补足语[3]长句。bring…intocontact使…接触，联系。[4]长句。It代表operatingsystem，为主语，它有三个并列的宾语。[5]Java2Platform,EnterpriseEdition(缩写为J2EE)，是一个独立平台，是由Sun公司为开发、构建和使用基于Web网企业在线应用而推出的。WebSphereMQ,是IBM1992年公布的网络通信软件产品系列，后于2002年将其并入WebSphere。[6]ofsuch……介词短语作表语；that引导的是同位语从句[7]numericaladdresses即IP地址EXERCISESMultipleChoices:1.Operatingsystemsandmiddleware.a.havelessincommonb.bothcansupportothersoftwarec.havemuchincommond.bothcansupportapplicationprogramsb,c,d2.AnoperatingsystemprovidestheservicesinitsAPIby.a.usingthefeaturesofthehardwareb.offeringdatabaseaccessibilityc.usingdiskdrive’sabilityd.offeringfixed-lengthblocksofdataa,c,d3.AmiddlewareprovidestheservicesinitsAPIbyusing.a.thefeaturesofanunderlyingoperatingsystemb.anoperatingsystemtoaccessrelationaldatabasec.diskdrivesabilityd.anoperatingsystemtoreadandwritefilesinthedatabasea,b,d4.Middlewareliesin.a.thetopofthelayeringverticalstackb.themiddleofthelayeringverticalstackc.thetopofanoperatingsystemd.themiddleofinteractionsbetweendifferentapplicationprograms5.Thefollowingproductsofsoftw