外文翻譯--基于Java的訪問遠程數(shù)據(jù)庫的高效的標準軟件體系結(jié)構(gòu) 英文版.pdf

FutureGenerationComputerSystems15(1999)417424EfficiencyofstandardsoftwarearchitecturesforJava-basedaccesstoremotedatabasesN.Zingirian,M.Maresca,S.NalinDipartimentodiElettronicaedInformatica,UniversityofPadua,Padua,ItalyAccepted14December1998AbstractNovelclientserverarchitecturesforremotedatabaseaccessareincreasinglytakingadvantageofWebtechnology,adoptingWebbrowsersasgraphicuserinterfacesintheclientsandtraditionalSQLdatabasemanagementsystems(DBMSs)intheservers.Theinter-operationbetweenstandardbrowsersandspecificDBMSsistodaysupportedbyanumberofsoftwarearchitecturesbasedontheJavavirtualmachineembeddedinlastgenerationbrowsers.Unfortunatelysuchsoftwarearchitec-tures,whichappearexcellentfromthepointsofviewofopennessandflexibility,introduceconspicuouslatenciesindatabaseaccess.Theobjectiveofthispaperistoidentifysuchlatenciesthroughtheanalysisofanumberofexperimentalresults.ThepaperdescribesfourdifferentsoftwarearchitecturessupportingJava-basedSQLdatabaseaccess,reportstheirperformancemeasurementsondifferenthardwareplatformsandcomparestheresultsobtained.c1999ElsevierScienceB.V.Allrightsreserved.Keywords:CORBA；Java；JDBC；Performanceevaluation；Visualdatabaseaccess1.IntroductionThetraditionalapproachtoclientserverdatabaseaccessisbasedonthecombinedactionofauserinterfacewritteninavisuallanguage(i.e.theclient)andastandardSQLengine(i.e.theserver).Currently,thisapproachischallengedbynovelsolutionsbasedontheemergingWebparadigm1.IntheWeb-basedsolutionstheuserinterface,typicallywritteninJava,isdownloadedbyabrowserfromtheserverandrunsonthebrowservirtualmachine.Themainpointofsuchsolutionsisthattheclientsoftwareresidesintheserversystemasauniquecopy,ratherthanbeingreplicatedintheclientsystems.Thisfactallowsthecostsofinstallation,configurationandmaintenanceoftheclientsoftwaretobereducedthankstothepossibilityofcentralisingalltheseoperationsattheserversite2.Web-basedaccesstoSQLdatabasescanbesupportedbyanumberofsoftwarearchitectures3characterizedbyadifferentcompositionofasetofbasiccomponents4.Unfortunatelysuchsoftwarearchitectures,whichappearexcellentfromthepointofviewofopennessandflexibility,introduceconspicuouslatenciesindatabaseaccess.Correspondingauthor.0167-739X/99/$seefrontmatterc1999ElsevierScienceB.V.Allrightsreserved.PII:S0167-739X(98)00085-5418N.Zingirianetal./FutureGenerationComputerSystems15(1999)417424Fig.1.Softwarearchitecture1:databaseaccessthroughJavasockets.TheobjectiveofthestudypresentedinthispaperistodescribefourdifferentsoftwarearchitecturesimplementingWeb-basedSQLdatabaseaccessandtoreportandcomparetheirperformances,characterizingthesourcesofthelatenciesintroducedbyeacharchitecture.Thepaperisorganizedasfollows.FirstwedescribethestandardsoftwarearchitecturesforJava-baseddatabaseaccess(Section2).Thenwepresentthetestbedusedandthemethodologyfollowedinourexperiments(Section3).Finallywepresenttheresultsoftheexperiments(Section4)anddiscusstheperformanceprofileofthesoftwarearchitecturestested(Section5).Abriefsummary(Section6)concludesthepaper.2.SoftwarearchitecturesforJava-baseddatabaseaccessInthissectionwepresentthefoursoftwarearchitecturesforJava-baseddatabaseaccessthatweselectedforourinvestigation.Eacharchitecturecomplieswiththeclientserverparadigmandconsistsofthreemainentities:theclient,theserverandtheinter-operabilitycomponents.Theclientandtheserverarethesameineacharchitecture；theinter-operabilitycomponentsarethedistinctivefeatureforeacharchitecture.TheclientisaJava-enabledbrowser,theserverisaSQLdatabasemanagementsystem(DBMS)whichacceptsremotenetworkconnectionsandqueries.WeassumethatthenetworkprotocolstackisbasedontheTCP/IPprotocolsuite.Theinter-operabilitycomponentsofeachsoftwarearchitecturearedescribedintherestofthesection.2.1.ArchitecturebasedonJavasocketconnectivitymodulesTheschemeofthearchitecturebasedonJavasocketconnectivitymodulesisdepictedinFig.1Theshadedblocksrepresentthesoftwaremodulesthattheprogrammerhastodeveloptointerconnecttheexistingcomponents.Theclient(browser)downloadsanappletfromtheservermachineandrunsit.TheappletsendsthequeriesandreceivestheresponsesthroughtheJavasocketmodules.Theserver(DBMS)exchangesdatawiththeclientthroughasoftwarecomponentthatactsasanintermediatecustomagent.SuchanintermediatecustomagentreceivestheclientqueriesandsubmitsthemtothedatabasethroughthedatabaseAPIlibrary.TheconnectivitybetweentheappletandthecustomagentisbasedonTCP/IP.OntheclientsidecommunicationissupportedbythestandardJavasocketAPI；ontheserversidecommunicationissupportedbythestandardUNIXsocketinterface.Inter-operationbetweentheappletandthecustomagentisbasedonacustomprotocolwhichsupportsthefundamentaldatabaseaccessoperations(opendatabase,submitquery,retrieveresponse,closedatabase).2.2.ArchitecturebasedonproprietaryDBMSJDBCdriverTheArchitecturebasedonproprietaryDBMSJDBCdriverisdepictedinFig.2.JavadataBaseconnectivity(JDBC)isastandardinterfacewhichallowsJavaappletsandapplicationstointer-operatewithdatabase.LikeinN.Zingirianetal./FutureGenerationComputerSystems15(1999)417424419Fig.2.SoftwarearchitecturefordatabaseaccessbasedonDBMSproprietaryJavaJDBC.Fig.3.SoftwarearchitecturefordatabaseaccessbasedonJavaJDBCandrequestbroker.thepreviousarchitecture,theclient(browser)downloadsanappletfromtheservermachineandrunsit.TheappletaccessestheDBMSthroughthestandardprimitivesoftheJBDBCapplicationprogramminginterface(JDBCAPI).TheJDBCAPIisavailableasapartofthestandardclassesoftheJavadeveloperkitsandoftheJava-enabledbrowserscompliantwitthelatestversionsofJava.TheJDBCclassesarenotspecificforanyparticularDBMS,exceptforoneclass,denotedtheJDBCdriver,whichimplementsthecommunicationprotocolrequiredbythespecificDBMSwhichitrefersto.ThespecificJDBCdriversareprovidedbytheDBMSvendorsorbythirdpartiesandaredynamicallylinkedtothestandardJDBCobjects.UsuallytheJDBCdriverisdownloadedfromtheserveralongwiththeclientapplet.TheDBMSdriverinteroperateswiththeDBMSoverthenetworkbytranslatingtheJDBCmethodsinproprietarymessagestoproprietaryservicerequestmessages.Theserver(DBMS)receivesthequeries,sendstheresponsesandperformsalltheoperationsthroughitsproprietaryprotocol,withnoneedofadditionalinter-operabilitymodulesintheservermachine.2.3.ArchitecturebasedonJDBCrequestbrokermiddlewareThearchitecturebasedonarequestbrokerisdepictedinFig.3.Asinthepreviousarchitecture,theappletcommunicateswiththedatabasethroughthestandardJDBCAPIandthroughaspecificJDBCdriver.Asopposedtothepreviousarchitecture,theJDBCdriverdoesnotaccessthedatabasedirectlybutitaccessanintermediateobject,calledthebroker,runningontheservermachine,throughaproprietaryprotocol.Whentheappletrequestsaconnection,therequestbrokerdynamicallyinstantiatestwocomponents:aJDBCagent,andadatabaseagentspecificfortheDBMSadopted.Theserver(DBMS)andtheclientinter-operatethroughthedatabaseagentandthroughtheJDBCagentwhichinteractbymeansofaproprietaryprotocol.Theopennessandflexibilityadvantagesofusingtherequestbrokerandtheagentsarediscussedin5.420N.Zingirianetal./FutureGenerationComputerSystems15(1999)417424Fig.4.SoftwarearchitecturefordatabaseaccessbasedonCORBA.Table1SoftwareproductsusedascomponentsofthetestedsoftwarearchitecturesSoftwarecomponentSoftwareproductVendorDBMS1PostgreSQL6.1.1UniversityofCalifornia7BrowserNavigator4NetscapeJ.socketNetscapeDBMSJDBCdriverclasspostgresql.driverUniversityofCaliforniaRequestbrokeroplrqbOpenlinkDatabaseagentpgr95svOpenlinkJDBCagentjdbcsvOpenlinkBrokerJDBCDriverclassopenlink.driverOpenlinkClientORBpackageorg.omg.CORBAVisigenic/NetscapeServerORBomniORB2Olivetti&OracleResearchLabs2.4.ArchitecturebasedonCORBAinter-operabilitycomponentsTheCORBA-basedarchitectureisshowninFig.4.EveninthiscasetheappletcommunicateswiththeDBMSthroughanobject-orientedAPI.ThisAPIinstantiatesandinter-operateswithadatabaseaccessobjectwhichresidesintheservermachine.Inter-operabilityissupportedbyapairoflibrariescalledobjectrequestbrokers(ORBs)6whichcommunicatethroughtheInternetInter-ORBprotocol(IIOP).OneORBisaJavapackagelocatedintheclientmachinewhiletheotherORBisalibrarylocatedintheservermachine.Theserver(DBMS)communicateswiththedatabaseaccessobjectthroughtheDBMSapplicationprogramminginterface.ThedatabaseaccessobjectisdevelopedbythesystemintegratoranditsAPIisdescribedthroughaformalspecificationlanguagedenotedasinerfacedescriptionlanguage(IDL).TheIDLsup