Estimating the quality of data in relational databases(4)
时间:2025-04-04
时间:2025-04-04
3SoundnessandCompletenessasMeasuresofData
Quality
Wede netwomeasuresofdataqualitythataregeneralenoughtoencompassmostexistingmeasuresandaspectsofdataquality[5,19].Thebasicideasunderlyingthesemeasureswere rststatedin[7].Inthatpapertheauthorsuggestedthatdeclarationsoftheportionsofthedatabasethatareknowntobeperfectmodelsoftherealworld(andtherebytheportionsthatarepossiblyimperfect)beincludedinthede nitionofeachdatabase.Withthisinformation,thedatabasesystemcanqualifytheaccuracyoftheanswersitissuesinresponsetoqueries:eachanswerisaccompaniedbystatementsthatde netheportionsoftheanswerthatareguaranteedtobeperfect.Thisapproachusesviewstospecifytheportionsofthedatabaseortheportionsofanswersthatareperfectmodelsoftherealworld.
Morespeci cally,thisapproachinterpretsinformationquality,whichittermsintegrity,asacombinationofsoundnessandcompleteness.Adatabaseviewissoundifitincludesonlyinformationthatoccursintherealworld;adatabaseviewiscompleteifitincludesalltheinformationthatoccursintherealworld.Hence,adatabaseviewhasintegrity,ifitincludesthewholetruth(completeness)andnothingbutthetruth(soundness).Aprototypedatabasesystemthatisbasedontheseideasisdescribedin[10].Theseideaswerefurtherdevelopedin[9]andaresummarizedbelow.
GivenadatabaseschemeD,weassumetheexistenceofahypotheticaldatabaseinstanced0thatcapturesperfectlythatportionoftherealworldthatismodeledbyD(theidealortruedatabase).Inaddition,weassumeoneormoreactualinstancesdi(i≥1).Theactualinstancesareconsideredapproximationsoftheidealinstanced0.
GivenaviewV,wedenotebyv0itsextensionintheidealdatabased0(theidealortrueextensiontoV)andwedenotebyviitsextensionintheactualdatabasedi.Again,theextensionsviareapproximationsoftheidealextensionv0.
ConsiderviewV,itsidealextensionv0,andanapproximationv.Ifv v0,thenvisacompleteextension.Ifv v0,thenvisasoundextension.Obviously,anextensionwhichissoundandcompleteistheidealextension.
Withthesede nitions,eachviewextensioniseithercompleteorincomplete,andeithersoundornonsound.Wenowre nethesede nitionsbyassigningeachextensionavaluethatdenoteshowwellitapproximatestheidealextension.Weshalltermthisvaluethegoodnessoftheextension.Werequirethatthegoodnessofeachextensionbeavaluebetween0and1,thatthegoodnessoftheidealextensionbe1,andthatthegoodnessofextensionsthatareentirelydisjointfromtheidealextensionbe0.Formally,agoodnessmeasureisafunctiongonthesetofallpossibleextensionsthatsatis es
v:g(v)∈[0,1]
v:v∩v0= = g(v)=0
g(v0)=1
…… 此处隐藏:413字,全部文档内容请下载后查看。喜欢就下载吧 ……上一篇:三结合教育工作总结
下一篇:理性的批判和道义的批判