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1、英文文献ObjectpersistenceandJavaByArsalanSaljoughy,JavaWorld.com,05/01/97Objectdurability,orpersistence,isthetermyouoftenhearusedinconjunctionwiththeissueofstoringobjectsindatabases.Persistenceisexpectedtooperatewithtransactionalintegrity,andassuchitissubjec

2、ttostrictconditions.(SeetheResourcessectionofthisarticleformoreinformationontransactionprocessing.)Incontrast,languageservicesofferedthroughstandardlanguagelibrariesandpackagesareoftenfreefromtransactionalconstraints.Aswe'llseeinthisarticle,evidencesugge

3、ststhatsimpleJavapersistencewilllikelystemfromthelanguageitself,whilesophisticateddatabasefunctionalitywillbeofferedbydatabasevendors.NoobjectisanislandIntherealworld,yourarelyfindanobjectthatlacksrelationstootherobjects.Objectsarecomponentsofobjectmodel

4、s.Theissueofobjectdurabilitytranscendstheissueofobjectmodeldurabilityanddistributiononcewemaketheobservationthatobjectsareinterconnectedbyvirtueoftheirrelationstooneanother.Therelationalapproachtodatastoragetendstoaggregatedatabytype.Rowsinatablerepresen

5、tthephysicalaggregateofobjectsofthesametypeondisk.Therelationshipsamongobjectsarethenrepresentedbykeysthataresharedacrossmanytables.Althoughthroughdatabaseorganization,relationaldatabasessometimesallowtablesthatarelikelytobeusedtogethertobeco-located(orc

6、lustered)inthesamelogicalpartition,suchasadatabasesegment,theyhavenomechanismtostoreobjectrelationshipsinthedatabase.Hence,inordertoconstructanobjectmodel,theserelationshipsareconstructedfromtheexistingkeysatruntimeinaprocessreferredtoastablejoins.Thisis

7、thesamewell-knownpropertyoftherelationaldatabasescalleddataindependence.Nearlyallvariantsofobjectdatabasesoffersomemechanismtoenhancetheperformanceofasystemthatinvolvescomplexobjectrelationshipsovertraditionalrelationaldatabases.Toqueryortonavigate?Insto

8、ringobjectsondisk,wearefacedwiththechoiceofco-locatingrelatedobjectstobetteraccommodatenavigationalaccess,ortostoreobjectsintable-likecollectionsthataggregateobjectsbytypetofacilitatepredicate-basedaccess(queries),orboth.T