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1、数据抽取(Dataextraction)DataextractioncatalogDefinitionDataextractionmethodusesrelationaldatabasefordatasourceDatasourcenonrelationaldatabaseExpansiondefinitionDataextractionmethodusesrelationaldatabasefordatasourceDatasourcenonrelationaldatabaseEdittheparagraphdef
2、initiondataextractionistheprocessofextractingdatafromthedatasource.Editthisparagraphdataextractionway,datasourceusingrelationaldatabaseInpracticalapplication,therelationaldatabaseisusedformoredatasources.Extractingdatafromthedatabasegenerallyhasthefollowingways
3、.(1)theamountofextractiontotalextractionsimilartothedatatransferorcopythedata,itwillbeatableorviewinthedatasourcedatafromthedatabaseofthewhollyintactextractedandconvertedintotheirownETLtoolscanidentifytheformat.Totalvolumeextractionisrelativelysimple.(2)increme
4、ntalextractionincrementalextractiononlyextractsnew,modifiedanddeleteddatafromthetablestobeextractedfromthedatabasesincethelastextraction.IntheprocessofusingETL.Incrementalextractionismorewidelyusedthantotalamountextraction.Howtocapturethechangingdataisthekeytoi
5、ncrementalextraction.Generally,therearetworequirementsforcapturemethod:accuracy,accuratecaptureofchangedatainthebusinesssystem;performance,minimizethepressureonthebusinesssystem,affecttheexistingbusiness.Thecurrentmethodofcapturingchangedatausedinincrementaldat
6、aextraction:A.trigger:toestablishtriggersintheselectedtable,toestablishageneralinsert,modifyanddeletethreetriggers,whensourcedatainthetableischanged,thecorrespondingtriggerwillchangethedataintoatemporarytable.Dataextractionthreadfromthetemporarytableextraction.
7、Theadvantageofflipflopisthehighperformanceofdataextraction.Thedisadvantageisthatthetriggerisrequiredtobesetupinthebusinessdatabase,whichhasacertainimpactontheperformanceofthebusinesssystem.B.timestamp:itisakindofincrementalincrementaldataacquisitionmethodbasedo
8、ndatacomparison,addatimestampfieldinthesourcetable,systemupdatetabledata,modifythetimestampfieldvalueatthesametime.Whendataextractionisdone,whatdataisextractedbycomparingthe