Estimating the quality of data in relational databases(3)

2OverallApproach

Ouroverallapproachforachievingthegoalsthatwerestatedintheintroductioncanbedescribedasasequenceofproblems.

Webegin,inSection3,bydescribingthedualmeasuresthatwillbeusedtogaugethequalityofdatabaseinformation.Weclaimthatthesemeasurescaptureinamostnaturalway,therelationshipofthestoredinformationtotruth,andarethereforeexcellentindicatorsofquality.

Ourmeasuresrequiretheauthenticationofdatabaseinformation,whichisaprocessthatneedstobedonebyhumans.However,weadvocatetheuseofstatisticalmethods(essentially,sampling)tokeepthemanualworkwithinacceptablelimits.ThissubjectisdiscussedinSection4.1.

Havingobtainedaccurateinformationaboutthequalityofthesamples,weproceedtopartitionthegivendatabasetoasetofcomponentsthatarehomogeneouswithrespecttoourqualitymeasures.Wethenestimatethequalityofthesecomponents,usingthesamples.Thisimpliesthatwheninformationisextractedfromasinglecomponent,itsqualityratingsareinheritedfromthecontainingcomponent.Thesemethods,describedinSections4.2and4.3,provideuswithqualityspeci cationsforthegivendatabases.

Finally,inSection5,wedescribetheprocessofinferringthequalityofanswerstoarbi-traryqueriesfromthequalityspeci cationsthathavebeenassignedtothedatabase.Ourtreatmentoftheproblemisinthecontextofrelationaldatabases,andweassumethestandardde nitionsoftherelationalmodel[17].Inparticular,thedatabasecomponentsmentionedearlierarede nedusingthemechanismofviews.Wealsomakethefollowingassumptions.

1.Queriesandviewsuseonlytheprojection,selection,andCartesianproductoperations,selectionsuseonlyrangeconditions,andprojectionsalwaysretainthekeyattribute(s).

2.Thestoredinformation(thedatabaseinstances)arerelativelystatic,andhencethequalityofdatadoesnotchangefrequently.

Becauseofspacelimitations,severalkeyissuesandsolutionsareonlysketchedinthispaper,andfullerdiscussionsareprovidedin[11].