面向对象的分布式系统语义多粒度锁定模式(IJITCS-V5-N5-10)

I.J.InformationTechnologyandComputerScience,2013,05,74-84PublishedOnlineApril2013inMECS()DOI:10.5815/ijitcs.2013.05.10Copyright©2013MECSI.J.InformationTechnologyandComputerScience,2013,05,74-84SemanticMulti-granularLockModelforObjectOrientedDistributedSystemsV.GeethaDepartmentofInformationTechnology,PondicherryEngineeringCollege,Puducherry,IndiaE-mail:[e-mail]uterScience&Engineering,PondicherryEngineeringCollege,Puducherry,IndiaE-mail:[e-mail]—Inobjectorienteddistributedsystems(OODS),theobjectsareviewedasresources.Concurrencycontroltechniquesareusuallyappliedonthedatabasetier.Thishasthelimitationsoflackofsupportoflegacyfilesandrequirementofseparateconcurrencycontrolmechanismsforeachdatabasemodel.Henceconcurrencycontrolontheobjectsatservertierisexplored.Toimplementconcurrencycontrolontheobjectsparticipatinginasystem,theimpactofmethodtypes,propertiesandclassrelationshipsnamelyinheritance,associationandaggregationaretobeanalyzed.Inthispaper,thetypesandpropertiesofclassesandattributesareanalysed.Thesemanticsoftheclassrelationshipsareanalysedtoascertaintheirlockmodes,granulesizesfordefiningconcurrencycontrolinOODS.Itisalsointendedtoproposecompatibilitymatrixamongalltheseobjectrelationships.IndexTerms—ObjectOrientedDistributedSystems,ConcurrencyControl,MultiGranularLockModel,ClassRelationships,DesignTimeTransactions,RunTimeTransactionsI.IntroductionObjectOrientedDatabaseManagementSystems(OODBMS)providesbettercomplexdatamodelingsupportforthenewlyemergingdistributedapplicationsthanrelationaldatabases.OODBMSisusedaspersistentdatastorefordistributedsystems.Itresidesinthedatabasetier.Howeverindistributedsystems,theservertierisimplementedasprocedures.Thisrequiresaconversionbetweenproceduralparadigmtoobjectorientedparadigmandviceversaforallthecommunicationsbetweenservertieranddatabasetier.Furthereachofthedatabasemodelsindistributedsystemshasitsownconcurrencycontrolmechanismsthatcannotbeadaptedtoanyoftheothermodels.Theconcurrencycontrolpoliciesaredefinedonlyforthedatabasetier.Theservertierhasnocontrolovertheconcurrencycontrol.Thisintroducesarestrictionofusingonlytherefinedpersistentdatastoreforthedomaindatalikedatabasemanagementsystems.Primitivedatastoreslikefilesarenotsupportedindistributedsystemsandhencetheycannotbereused.TheabovelimitationscanbeovercomeinOODS.InOODS,theservertierisalsoimplementedasobjects.Sotheconversionofdataformatbetweenservertieranddatabasetierisnotnecessary,ifOODBMSprovidespersistentdatastorage.Howeverconversionofdataformatisrequired,ifotherdatabasemodelsareused.Hencethepossibilityofprovidingacommonconcurrencycontrolmechanismthatisindependentofthepersistentdatastoretypeisexploredin[1]byshiftingtheconcurrencycontrolfromdatabasetiertoservertier.InOODS,objectsarethereusabledatasources.Theclientscanaccessthedatafromthedatastoreindatabasetieronlythroughtheobjectsintheservertier.Henceacommonconcurrencycontrolmechanismcanbedefinedfortheobjectsintheservertier.Theotheradvantageofthisshiftintheconcurrencycontroltotheservertierallowsusageoflegacydatastores.Alreadysemanticconcurrencycontrolmechanismshavebeenproposedforobjectorienteddatabasesbyexploitingtheobjectorientedparadigmfeatures.Theyout-performtheconventionalconcurrencycontrolmechanismsforOODBMS.HencethefeasibilityofextendingthesamemechanismstoOODSmaybeanalyzed.OODSsupportcontinuouslyevolvingdomainsinwhichtheservicesarefrequentlyenhancedtoprovidebetterclientsupport.Hencetransactionsprovidingruntimeservices(runtime)anddesignupdates(designtime)aretobesupported.ThoughconcurrencycontrolmechanismsinOODBMScanbeconsidered,theycannotbeextendedastheyareinOODS.Thisisbecausequerylanguagesareusedtoaccessdatabases.ButinOODS,objectorientedprogramminglanguageslikeC++,Javaareusedtomakeclientrequests.ThenlocktypesandSemanticMulti-granularLockmodelforObjectOrientedDistributedSystems75Copyright©2013MECSI.J.InformationTechnologyandComputerScience,2013,05,74-84granularitiesofresourcesaretobeascertainedfromtheclientcode.ThedoctoolslikedocC++,Javadoccanbeusedforidentifyingthemethodtypeandproperties.Followingthis,thecompatibilitymatrixusedinOODBMScanbeconsideredforadoptioninOODS.InOODBMS,lockmodesaredefinedonlyforconcreteclasses.Thelockmodesforabstractclassesarenotascertained.ThecompatibilitymatricesforinheritanceandaggregationhavebeendefinedforOODBMS.Tousethosematrices,locktypesandgranulesizesaretobedeterminedforinheritanceandaggregation(composition)usingtheclassificationofclassmethodtypesandpropertiesproposedin[2,3].Associationisonetheimportantrelationshipsfrequentlyusedtorelateobjectsparticipatinginadomain.In[4],theyhaveproposeddirectedgraphbasedassociationalgebraforqueryprocessingandoptimizationofobjectsinobjectorienteddatabases.Butsofar,thetypes,propertiesandattributesofassociationhavenotbeenexploredfortheirprobableimpactonconcurrencyorconcurrencycontrol.Thelockmodes,granulesizesandlockcompatibilityforassociationhavenotbeenexploredsofar.Inthefollowingsection,asemanticconcurrencycontroltechniqueis