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14DigitalLibrariesandWeb-BasedInformationSystemsIanHorrocksDeborahL.McGuinnessChristopherWeltyAbstractIthaslongbeenrealisedthatthewebcouldbene tfromhavingitscontentunder-standableandavailableinamachineprocessableform,anditiswidelyagreedthatontologieswillplayakeyroleinprovidingmuchenablinginfrastructuretosupportthisgoal.Inthischapterwereviewbrieyaselectedhistoryofdescriptionlogicsinweb-basedinformationsystems,andthemorerecentdevelopmentsrelatedtoOIL,DAML+OILandthesemanticweb.OILandDAML+OILareontologylanguagesspeci callydesignedforuseontheweb;theyexploitexistingwebstandards(XML,RDFandRDFS),addingtheformalrigorofadescriptionlogicandtheontologicalprimitivesofobjectorientedandframebasedsystems.14.1BackgroundandHistoryTheresearchworldaswellasthegeneralpublicareuni edintheiragreementthatthewebwouldbene tfromsomestructureandexplicitsemanticsforatleastsomeofitscontent.Numerouscompaniesexisttodaywhoseentirebusinessmodelisbasedonprovidingsomesemblanceofstructureandconceptualsearch(i.e.yellowpagesandsearch).ToparaphraseA.A.Milne,\Providingstructureisoneofthethingsdescriptionlogicsdobest![Milne,1928].Inthischapterwereviewbrieythehistoryofdescriptionlogicsinweb-basedinformationsystems,andthemorerecentdevelop-mentsrelatedtoOIL(theOntologyInferenceLayer),DAML(theDARPAAgentMarkupLanguage),DAML+OILandthe\semanticweb.Thewebhasbeenacompellingplaceforresearchactivityinthelastfewyears,andaswecannotcoverallthemanye ortswewillchooseafewexemplare ortsthatillustratesomeofthekeyissuesrelatedtodescriptionlogicsontheweb.1214.1.1UntangleTherelationshipbetweenhypertextandsemanticnetworkshaslongbeenrealized,butoneoftheearliestdescriptionlogicsystemstorealizethisrelationshipwastheUntanglesystem[WeltyandJenkins,2000],adescription-logicsystemforrepresent-ingbibliographic(card-catalog)information.TheUntangleProjectbeganasabitofexploratoryresearchinusingdescriptionlogicsfordigitallibraries[Welty,1994],butoutofsheertemporalcoincidencewiththeriseoftheweb,awebinterfacewasaddedandthe rstweb-baseddescriptionlogicsystemwasborn.TheoriginalUntanglewebinterfacewasdevelopedin1994[Welty,1996a],andcombinedLisp-ClassicandtheCommon-LispHypermediaServer(CL-HTTP)[Mallery,1994]toimplementahypertextviewoftheABoxandTBoxsemanticnetworks,andusednestedbulletliststoviewtheconcepttaxonomy,within-pagecrossreferencesforconceptshavingmultipleparents.Theinterfacewasinterest-inginsomerespectsasatooltovisualizedescriptionlogicandsemanticnetworkinformation,thoughthisaspectwasneverfullydeveloped.TheresearchintheUntangleprojectwastoapplydescriptionlogicstoprob-lemsindigitallibraries,speci callytheclassi cationandretrievalofcardcataloginformation.Intheearlydaysofdescriptionlogicapplications,researchersscouredtheworldfortaxonomies.Oneplacewithwell-developedtaxonomiesarelibrarysubjectclassi cationsschemes,suchastheDeweyDecimalSystem.TheUntangleprojectsoughttoutilizedescriptionlogicstoformallyrepresenttheestablishedandwell-documentedprocessesbywhichbooksareclassi edbysubject,withthegoalofprovidingatooltoimproveaccuracyandincreasethethroughputofclassi cation.Thepromiseofdigitallibrariesclearlyseemedtoimplythattheentirelyhuman-basedsystemofsubjectclassi cationwouldbecomebackloggedandahindrancetopublication.Whilethemaincontributionoftheworkwasactuallyintheareaofdigitallibraryontologies,ithadseveralusefulimplicationsfordescriptionlogics.Forconceptualmodeling,thesystemmadecleartheverypracticalusesforprimitiveandde nedconceptsasbasicontologicalnotions.Primitiveconceptscanbeusedinamodeltorepresentclassesofindividualsthatusersareexpectedtobeabletoclassifynaturally.De nedconceptscanbeusedinamodeltorepresentsubclassesoftheprimitiveonesthatthesystemwillbeabletoclassifyifneeded.Forexample,inlibrariesweexpectalibrariantoberesponsibleforrecognizingthedi erencebetweenabookandajournal.Suchadistinctionistrivial.Ontheotherhand,theyarenotresponsibleforclassifyingabiography(thoughtheycan,ofcourse):abiographyissimplyabookwhosesubjectisaperson.AstheWorldWideWeb()becametheprimarymeansofdisseminationofcomputerscienceresearch,thegoalsoftheUntangleprojectshiftedin1995toDigitalLibrariesandWeb-BasedInformationSystems3catalogingandclassifyingpagesontheweb[Welty,1996b],whichwasviewedasamassiveandunstructureddigitallibrary[Welty,1998].AsimilarprojectbeganatroughlythattimeatAT&T,whosegoalwastoutilizeClassictorepresentataxonomyofwebbookmarks.Whileneverpublished,thisearlyworkbyTomKirkwaspartoftheinformationmanifoldproject[Levyetal.,1995].Kirk'svisualisationtoolswerealsousedinternallytoprovideadditionalvisualisationsupporttotheClassicsystem.Thisnewworkexposedsomeofthelimitationsofusingdescriptionlogicsformod-eling[Welty,1998].Onemusttrade-o utilizingautomatedsupportforsubsumptionwiththeneedtoreifytheconceptsthemselves.Forexample,theworkstartedwiththemotivationthatlibraryclassi cationschemeswerewell-developedtaxonomiesthatwouldbeappropriateforuseindescriptionlogics.Toutilizethepowerofsubsumptionreasoning,theelementsofthesubjecttaxonomymustobviouslybeconcepts.Somesubjects,however,arealsousefultoconsiderasindividu