zeos数据库对象概述sergey sereoukhov merlin overview.pdf

OverviewoftheZeosDatabase

ObjectsArchitecture

SergeySeroukhov

MerlinMoncure

26November2003(Updated29/5/2008byMarkDaems)

TableofContents

1.GeneralOverview2

2.PlainAPILayer2

3.DatabaseConnectivityLayer3

4.ComponentLayer5

5.Epilog6

DirectaccesstoSQLdatabasescontinuestobeavitaltechnologyevenintodaysenterpriseenvironment.Thou-

sandsoftwo-tierclientserverapplicationsaredevelopedandmaintainedintheinternationalbusinesscommu-

nity.Mostofthemarebuiltoffofspeciallydesignedapplicationprogramminginterfaces(APIs)toretrieverela-

tionaldataandexecuteSQLstatements.

Currently,thereisseveralstandardizedandwidelyusedAPIstoaccessSQLdatabases,suchasODBC,JDBC,

andADO.Borlandalsoreleasedtheirproprietarydatabasemiddlewareinterfaceforitsdevelopmenttools,

calledtheBorlandDatabaseEngine(BDE).DespitebeingfreelydistributedwithBorlandspopularlineofap-

plicationdevelopmenttools,theBDEwasunpopularbecauseofcomplexitiesininstallationandpoorperfor-

mance.AsDelphibecameoneoftheleadingapplicationdevelopmenttoolsfortheWindowsplatform,individu-

alsandcompaniesproposedalternativeinterfacestotheBDE.These“BDEAlternatives”optimizedaccessto

thedatabasebydirectlyusingthenativedatabasedriver,providingperformanceandfeatureadvantageswithre-

specttotheBDE.

RealizingthelimitationsoftheBDE,BorlandproposedanewtypeofdatabaseinterfacecalleddbExpress.This

interfacewasdesignedtobrokeraccessbetweenDelphiandvirtuallyanyrelationaldatabasethrough3rdparty

drivers.BorlandsignificantlyimprovedtheperformanceofdbExpresswithrespecttotheBDE,buttheimple-

mentationwasbuggyandsupportedonlyalimitedsubsetofSQLthathamperedfunctionality.

TheZeosDatabaseObjectcomponentlibrary(ZeosLib)isoneofthebest-knownBDEalternatives.Originally

thelibrarywasdevelopedforMySQLandPostgreSQLdatabases,butsupportforothervendorswassoon

added.Duringthedevelopmentprocess,certainlimitationso