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1、英文文献ObjectpersistenceandJavaByArsalanSaljoughy,JavaWorld.com,05/01/97Objectdurability,orpersistence,isthetermyouoftenhearusedinconjunctionwiththeissueofstoringobjectsindatabases.Persistenceisexpectedtooperatewithtransactionalintegrity,andassuchitissubjecttostrictcon
2、ditions.(SeetheResourcessectionofthisarticleformoreinformationontransactionprocessing.)Incontrast,languageservicesofferedthroughstandardlanguagelibrariesandpackagesareoftenfreefromtransactionalconstraints.Aswe'llseeinthisarticle,evidencesuggeststhatsimpleJavapersist
3、encewilllikelystemfromthelanguageitself,whilesophisticateddatabasefunctionalitywillbeofferedbydatabasevendors.NoobjectisanislandIntherealworld,yourarelyfindanobjectthatlacksrelationstootherobjects.Objectsarecomponentsofobjectmodels.Theissueofobjectdurabilitytranscen
4、dstheissueofobjectmodeldurabilityanddistributiononcewemaketheobservationthatobjectsareinterconnectedbyvirtueoftheirrelationstooneanother.Therelationalapproachtodatastoragetendstoaggregatedatabytype.Rowsinatablerepresentthephysicalaggregateofobjectsofthesametypeondis
5、k.Therelationshipsamongobjectsarethenrepresentedbykeysthataresharedacrossmanytables.Althoughthroughdatabaseorganization,relationaldatabasessometimesallowtablesthatarelikelytobeusedtogethertobeco-located(orclustered)inthesamelogicalpartition,suchasadatabasesegment,th
6、eyhavenomechanismtostoreobjectrelationshipsinthedatabase.Hence,inordertoconstructanobjectmodel,theserelationshipsareconstructedfromtheexistingkeysatruntimeinaprocessreferredtoastablejoins.Thisisthesamewell-knownpropertyoftherelationaldatabasescalleddataindependence.
7、Nearlyallvariantsofobjectdatabasesoffersomemechanismtoenhancetheperformanceofasystemthatinvolvescomplexobjectrelationshipsovertraditionalrelationaldatabases.Toqueryortonavigate?Instoringobjectsondisk,wearefacedwiththechoiceofco-locatingrelatedobjectstobetteraccommod
8、atenavigationalaccess,ortostoreobjectsintable-likecollectionsthataggregateobjectsbytypetofacilitatepredicate-basedaccess(queries),orboth.T
