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MetadatasupportforconnectingapplicationcomponentsasynchronouslyOliverSeidelPhDDissertation1999ChurchillCollege,UniversityofCambridge|MitDankanmeineEltern|PREFACEThisdissertationistheresultofmyownworkandincludesnothingwhichistheoutcomeofworkdoneincollaboration.xACKNOWLEDGEMENTSIwishtothankmysupervisorKenMoodyforhisexample,adviceandencouragementduringthelastfouryears.IwouldalsoliketothankthemembersoftheOPERAgroupformanyinspiringdis-cussions,andforprovidingsuchafriendlyworkingenvironment.MyparticularthanksgotoChaoyingMaandRichardHayton,whowerethemostexperiencedresearchersthatIsharedanocewith.AlanAbrahamsandAlexisHombrecherhavetakenalotoftimetocarefullyreadthedraftsforthisdissertationandhaveprovidedvaluablefeedback{thankyou.Manythanksgotomyparents,withoutwhosesupportandencouragementIwouldhavenevercomeheretoworktowardsadegree.IwouldalsoliketothankmygirlfriendBarbaraLieskeforenduringmyabsence.TheresearchcarriedoutforthisthesiswasfundedbytheUniversityofCambridgeComputerLaboratorySupporters’Club.xiiABSTRACTThetechnologicaladvancesofrecentyearshaveledtotheproliferationofnetworkingandinter-networking:whilenetworkingoriginallywasreservedtolargeinstallationsthatcouldaordtheassociatedhardwareandservicecosts,itnowhaswideappli-cationinrmsandevensomehomes.Inthecommercialcontext,onecanoftenndinstallationsthatarepervasivelynetworked,butseparatedfromtheoutsideworldbyasecuritygateway.Intheconsumercontext,itisalmostexclusivelythecasethatthetechnologyprovidesasymmetricchannelsintothehome.Whilethecurrentcropofapplicationsusesaclient-servermodelwithsynchronousinvocation,thenextgen-erationwillinvolvealargernumberofsimplermoduleswithmorespecicpurposes.Wirelessreportingandhomemonitoringaswellasbusinessprocessnoticationarelikelytouseasynchronoustechnology.Thesesystemswillonlyndacceptanceiftheyaresucientlyautomatedandrobust.Theyalsoneedtobeexibleenoughtocopewithamergingofpreviouslyindependentmanagementdomains.InthisdissertationIarguethatthemetadatadescribingthosesystemsmustbereadilyaccessibleinmachine-readableformfromwithinthesystem.Ifinformationdescribingtyping,theapplicationandthecongurationisavailable,greaterexibilitycanbeachieved,automationbecomespossibleandbettermonitoringimprovesrobustness.Iargueforawayofstructuringdataandmetadatathatallowsthemostimportantpartstobetreatedwiththereliabilityandtheassociatedperformancetrade-ooftransactions.Thisstructuringalsomakestheboundariesofautonomouscomponentsexplicit.Theresultantarchitectureissuitableforarangefromsimpletocomplexsystemsbyallowingtheomissionorinclusionofappropriatefunctionality.Duringthisresearchanappropriateformathasbeenchosentorepresentthemetadata.Thespecicationisavailableinformofanobjectmodel,withaconcretegrammar,andaframeworktoproducetheexecutablecodefromthedocumentation.Severalserialisa-tionregimesareavailable,tradingthespeedofbulkoperationsagainstthatofpartialupdatesandtradingspeedandsizeagainsthardwareindependence.Theserialisationregimecanbechangedonaper-invocationbasis.Signicanteortwentintotheper-sistencecomponent,whichfeaturescleaninterfacestoatorhierarchicalvariable-sizesegmentsandintegrateswithahigh-performanceloggingservice.Allcomponentshavebeendesignedtoprovidetransactionalguarantees,buttheactualtransactionmanagerimplementationonlysupportsalimitednumberofexecutionpaths.Therstphaseoftheprojectestablishedaexibleobjectpersistencemechanism,withspecialattentiontotheneedsofeventstreamstorage.Themetadataofeventswasthenspeciedbyestablishinganobjectdatabaseschema.Experimentstodene,storeandevolveaneventtypehierarchyhavebeencarriedoutsuccessfullyinthisframework.Inadditionasearchdirectorysystemhasbeentestedwhichcouldprovideyellowpagessupportforapplication-leveleventservices.Thisthesisproposesametadatabasedarchitectureforconnectingapplicationcomponentsasynchronouslyusingeventsasglue,andsuggestswherecomponentboundariescanbedrawnmosteectively.xivTYPOGRAPHICCONVENTIONSsampletextdescriptionofusageExampleforeignexpressionExamplecomputersourcecodeExamplecomputerscienceterminology‘Example’unusualusageofaword‘Examplephrase’unusualusageofaphraseExamplenameofaproductExamplenameofacompanyExamplenameofaninternationalstandardExamplenameofaninternationalstandardsorganisationxviCONTENTS1.Introduction::::::::::::::::::::::::::::::::::::12.Middlewareandmobileapplications:::::::::::::::::::::::72.1Overview...................................82.1.1ResearchEmphasis.........................82.1.2DistributedObjectSystems/RemoteExecution........82.1.3StandardsforDistributedComputing...............102.1.4Implementations..........................112.2Events....................................142.2.1MessageOrientedMiddleware(MOM)..............152.2.2TupleSpaces............................192.2.3EventSystems...........................232.3Directories,Traders,andSchemaRepositories..............302.3.1TheInternetDomainNameSystem................312.3.2SunMicrosystemsNIS+.......................322.3.3TheinternationalX.500electronicdirectorystandard......332.3.4Light-WeightDirectoryAccessPr