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1、英文文献ObjectpersistenceandJavaByArsalanSaljoughy,JavaWorld.com,05/01/97Objectdurability,orpersistence,isthetermyouoftenhearusedinconjunctionwiththeissueofstoringobjectsindatabases.Persistenceisexpectedtooperatewithtransactionalintegrity,andassuchitissubjecttostrictconditions.(Seet
2、heResourcessectionofthisarticleformoreinformationontransactionprocessing.)Incontrast,languageservicesofferedthroughstandardlanguagelibrariesandpackagesareoftenfreefromtransactionalconstraints.Aswe'llseeinthisarticle,evidencesuggeststhatsimpleJavapersistencewilllikelystemfromthel
3、anguageitself,whilesophisticateddatabasefunctionalitywillbeofferedbydatabasevendors.NoobjectisanislandIntherealworld,yourarelyfindanobjectthatlacksrelationstootherobjects.Objectsarecomponentsofobjectmodels.Theissueofobjectdurabilitytranscendstheissueofobjectmodeldurabilityanddis
4、tributiononcewemaketheobservationthatobjectsareinterconnectedbyvirtueoftheirrelationstooneanother.Therelationalapproachtodatastoragetendstoaggregatedatabytype.Rowsinatablerepresentthephysicalaggregateofobjectsofthesametypeondisk.Therelationshipsamongobjectsarethenrepresentedbyke
5、ysthataresharedacrossmanytables.Althoughthroughdatabaseorganization,relationaldatabasessometimesallowtablesthatarelikelytobeusedtogethertobeco-located(orclustered)inthesamelogicalpartition,suchasadatabasesegment,theyhavenomechanismtostoreobjectrelationshipsinthedatabase.Hence,in
6、ordertoconstructanobjectmodel,theserelationshipsareconstructedfromtheexistingkeysatruntimeinaprocessreferredtoastablejoins.Thisisthesamewell-knownpropertyoftherelationaldatabasescalleddataindependence.Nearlyallvariantsofobjectdatabasesoffersomemechanismtoenhancetheperformanceofa
7、systemthatinvolvescomplexobjectrelationshipsovertraditionalrelationaldatabases.Toqueryortonavigate?Instoringobjectsondisk,wearefacedwiththechoiceofco-locatingrelatedobjectstobetteraccommodatenavigationalaccess,ortostoreobjectsintable-likecollectionsthataggregateobjectsbytypetofa
8、cilitatepredicate-basedaccess(queries),orboth.T
