extendourmethodssothateachoperationdelivers,inadditiontoagoodnessestimateofitsresult,thenecessarybasesforfutureoperations.Thisprovidesuswiththeabilitytoperformsequencesofoperations.
Alegitimatequestionatthispointiswhethertheseestimatesdependontheorderinwhichtheyarecomputed,i.e.,whethertheestimatesofthegoodnessofequivalentrelationalalgebraexpressionsarethesame.Theanswertothisquestionisthattheestimatesareindependentoftheparticularexpressionused[11].
6ConclusionsandFutureResearch
Weintroducedanewmodelfordataqualityinrelationaldatabases,whichisbasedonthedualmeasuresofsoundnessandcompleteness.Thepurposeofthismodelistoprovideanswerstoarbitraryquerieswithanestimationoftheirquality.Weachievedthisbyadoptingtheconceptofabasis,whichisapartitionofthedatabaseintoviewsthatarehomogeneouswithrespecttothegoodnessmeasures.Thesebasesareconstructedusingdatabasesamples,whosegoodnessisestablishedmanually.Oncethebasesandtheirgoodnessestimatesareinplace,thegoodnessofanswerstoarbitraryqueriesisinferredrathersimply.
Weplantodevelopthecompletesetofproceduresforcalculatingsoundnessandcom-pletenessoftheanswerstootherrelationalalgebraoperations;i.e.,addproceduresforunion,di erence,andintersectionofviews.Oneofourmajorgoalsistousethesemethodstoesti-matethegoodnessofanswerstoqueriesagainstmultidatabases,wherethesamequerycouldbeanswereddi erentlybydi erentdatabases,andgoodnessinformationcanhelpresolvesuchinconsistencies.
Wehavealreadydiscussedtheadvantageofconsideringthecorrectnessofindividualattributesoverthecorrectnessofentiretuples.Still,anindividualvalueiseithercorrectorincorrect,and,whenincorrect,wedonotconsidertheproximityofastoredvaluetothetruevalue.Thisdirection,whichiscloselyrelatedtoseveraluncertaintymodelingtechniques,meritsfurtherinvestigation.
Becauseofthecostofestablishinggoodnessestimations,wehavenotedthatourmeth-odsaremostsuitableforstaticinformation.Whentheinformationisdynamic,itwouldbeadvisabletotimestamptheestimationsatthetimethattheywereobtainedandattachthesetimestampstoallqualityinferences.Onemayalsoconsidertheautomaticattenua-tionofqualityestimationsastimeprogresses.Thisdirectionisstilloutsideourimmediateobjectives.
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