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1、TemporalRDFClaudioGutierrez1,CarlosHurtado1,andAlejandroVaisman21DepartmentofComputerScienceUniversidaddeChile{cgutierr,churtado}@dcc.uchile.cl2DepartmentofComputerScienceUniversidaddeBuenosAiresavaisman@cs.toronto.edu1IntroductionTheResourceDescriptionFramework(
2、RDF)[16]isametadatamodelandlan-guagerecommendedbytheW3Cforbuildinganinfrastructureofmachine-readablesemanticsforthedataontheWeb,along-termvisionknownasSe-manticWeb.IntheRDFmodel,theuniversetobemodeledisasetofresources,essentiallyanythingthatcanhaveauniversalresou
3、rceidentifier,URI.Thelan-guagetodescribethemisasetofproperties,technicallybinarypredicates.De-scriptionsarestatementsverymuchinthesubject-predicate-objectstructure.Bothsubjectandobjectcanbeanonymousobjects,knownasblanknodes.Inaddition,theRDFspecificationincludesabu
4、ilt-invocabularywithanorma-tivesemantics(RDFS).Thisvocabularydealswithinheritanceofclassesandproperties,aswellastyping,amongotherfeatures[4].RDFSallowstowriteontologies,i.e.,descriptionsoftheconceptsandrelationshipsthatcanexistforacommunityofpeopleandsoftwareagen
5、ts,enablingknowledgesharingandreuseamongthem.Althoughsomestudiesexistaboutaddressingchangesinanontology[17],littleattentionhasdeservedtheproblemofrepresenting,updatingandqueryingtemporalinformationinRDF.Ofcourse,timeispresentinalmostanywebande-businessapplication
6、.Indeed,aspointedoutbyAbiteboul[1]themodelingoftimeisoneofthekeyprimitivesneededinaquerylanguageforWebandsemistructureddata.Thus,thereisaclearneedofapplyingtemporaldatabaseconceptstoRDFtoallowmetadatanavigationacrosstime.ConsideranRDFgraphdescribinginformationabo
7、utauniversity,asofitscreationtime,Figure1(left).Studentswereclassifiedastechnical,graduateorundergraduate,andtheonlygraduateprogramsofferedwereatthelevelof‘Mas-ter’studies(likeMBAorMSc);‘ProfessionalDiploma’wastheonlyprogramofferedatthetechnicallevel.Astheuniversity
8、evolved,thePh.Dprogramwascreated.Figure1(right)illustratesthenewsituation.Noticethedynamicsofthisexample:students(e.g.,John)canenrollinoneprogram(e.g.,Undergra
