1Introduction

Theimportanceofdataqualityintheinformationagecannotbeoverestimated.People,businesses,andgovernmentsrelymoreandmoreoninformationintheireverydayoperations,anddatabasesofdi erentkindsaretheprimarysourceofthisinformation.Ourdependenceondatabasesgrowssimultaneouslywiththeirsize,yetmostlargedatabasescontainerrorsandinconsistencies.Thereisagrowingawarenessinthedatabaseresearchcommunity

[13,19]andamongdatabasepractitioners[1]oftheproblemofdataquality.Bynow,theneedfordataqualitymetricsandformethodsforincorporatingthemindatabasesystemsiswellunderstood.Dataqualitycanbemetricizedinanumberofdi erentwaysdependingonwhichaspectofinformationareconsideredimportant[18,5].Theadditionofdataqualitycapabilitiestodatabasesystemswillenhancedecision-makingprocesses,improvethequalityofinformationservices,and,ingeneral,providemoreaccuratepicturesofreality.Ontheotherhand,thesenewcapabilitiesofdatabasesshouldnotbedemandingintermsofresources,e.g.,theymustnotaddtoomuchcomplexitytoqueryprocessingorrequiremuchmorememorythanexistingdatabases.

Therecentadvancesinthe eldofdataqualityconcerndataatanattributevaluelevel[18]andatarelationlevel[14].Thecomprehensivesurveyofthestate-of-the-artinthe eldisgivenin[19].Therelationalalgebraextendedwithdataaccuracyestimatesbasedontheassumptionsofuniformdistributionsofincorrectvaluesacrosstuplesandattributeswas rstdescribedin[14].

Withmoreandmoreelectronicinformationsourcesbecomingwidelyavailable,theissueofthequalityofthese,often-competing,sourceshasbecomegermane.Weproposeastandardforratinginformationsourceswithrespecttotheirquality.Animportantconsiderationisthatthequalityofinformationsourcesoftenvariesconsiderablywhenspeci careaswithinthesesourcesareconsidered.Thisimpliesthattheassignmentofasingleratingofqualitytoaninformationsourceisusuallyunsatisfactory.Ofcourse,totheuserofaninformationsourcetheoverallqualityofthesourcemaynotbeasimportantasthequalityofthespeci cinformationthatthisuserisextractingfromthesource.Therefore,methodsmustbedevelopedthatwillderivereliableestimatesofthequalityoftheinformationprovidedtousers,fromthequalityspeci cationsthathavebeenassignedtothesources.

Ourworkherebearsonalltheseconcerns.Wedescribeanapproachthatusesdualqualitymeasuresthatgaugethedistanceoftheinformationinadatabasefromthetruth.Wethenproposetocombinemanualveri cationwithstatisticalmethodstoarriveatusefulestimatesofthequalityofdatabases.Weconsiderthevarianceinqualitybyisolatingareasofdatabasesthatarehomogeneouswithrespecttoquality,andthenestimatingthequalityofeachseparatearea.Thesecompositeestimatesmayberegardedasqualityspeci cationthatwillbea xedtothedatabase.Finally,weshowhowtoderivequalityestimatesforindividualqueriesfromsuchqualityspeci cations.