Logic Programming and Nonmonotonic Reasoning

ThesearetheproceedingsoftheSixthInternationalConferenceonLogicP- grammingandNonmonotonicReasoning (LPNMR2001). The conference was heldinViennafrom17thto19thofSeptember,2001. Itwascollocatedwiththe JointGerman/AustrianConferenceonArti?cialIntelligence(24thGerman/9th AustrianConferenceonArti?cialIntelligence),KI2001. LPNMR conferences aim to promote research in logic-based programming languages, database systems, nonmonotonic reasoning, and knowledge rep- sentation. LPNMR2001 was the sixth conference in the series. The previous meetingswereheldinWashington,DC,in1991,inLisbon,Portugal,in1993,in Lexington,Kentucky,in1995,inDagstuhl,Germany,in1997,andinElPaso, Texas,in1999. ThetechnicalprogramofLPNMR2001wascomprisedof?veinvitedtalks thatweregivenbyJur .. genDix,GeorgGottlob,PhokionKolaitis,MaurizioLe- erini,andChiakiSakama. Italsocontained23technicalpresentationsselected bytheprogramcommitteeduringarigorousreviewprocess. Finally,asapart ofthetechnicalprogram,theconferencefeaturedaspecialsessioncomprisedof ninepresentationsanddemonstrationsofimplementednonmonotonicreasoning systems. Allthesecontributionsareincludedintheproceedings.Many individuals workedfor the success of the conference. Special thanks areduetoallmembersoftheprogramcommitteeandtoadditionalreviewers fortheire?ortstoproducefairandthoroughevaluationsofsubmittedpapers. Furthermore, we would like to thank the members of the Knowledge Based SystemsGroupoftheViennaUniversityofTechnology,whichtookcareofthe localorganization. Weparticularlyappreciatedthenevertiringe?ortofElfriede Nedoma,secretarytothegroup. WewouldalsoliketothankGerdBrewkafor hissupportiveroleinarrangingthecollocationoftheconferencewithKI2001. Last,butnotleast,wethankthesponsoringinstitutionsfortheirgenerosity.September2001 ThomasEiter WolfgangFaber Miros lawTruszczynski ' Conference Organization ProgramCo-chairs ThomasEiter(ViennaUniversityofTechnology,Austria) Miros lawTruszczynski ' (UniversityofKentucky,USA) ProgramCommittee AlexanderBochman(HolonAcademicInstituteofTechnology,Israel) PieroBonatti(Universit' adegliStudiMilano/Crema,Italy) GerhardBrewka(UniversityofLeipzig,Germany) JamesDelgrande(SimonFraserUniversity,Canada) MarcDenecker(KatholiekeUniversiteitLeuven,Belgium) NormanFoo(UniversityofNewSouthWales,Australia) MichaelGelfond(TexasTechUniversity,USA) KatsumiInoue(KobeUniversity,Japan) AntonisKakas(UniversityofCyprus) NicolaLeone(Universit' adegliStudidellaCalabria,Italy) VladimirLifschitz(UniversityofTexasatAustin,USA) FangzhenLin(TheHongKongUniversityofScienceandTechnology,China) VictorMarek(UniversityofKentuckyatLexington,USA) ZhangMing-Yi(GuizhouAcademyofSciences,China) IlkkaNiemel. a(HelsinkiUniversityofTechnology,Finland) Lu'?sMonizPereira(UniversidadeNovadeLisboa,Portugal) MarcoSchaerf(Universitad ' iRoma"LaSapienza,"Italy) TorstenSchaub(UniversityofPotsdam,Germany) FrancescaToni(ImperialCollege,London,U. K.) Li-YanYuan(UniversityofAlberta,Canada) Publicity Chair WolfgangFaber(ViennaUniversityofTechnology,Austria) Organization VII Additional Reviewers Jos'eAlferes MehmetOrgun CristinaBaroglio MauricePagnucco KrysiaBroda VivianaPatti MauriceBruynooghe NikolayPelov FrancescoBuccafurri GeraldPfeifer CarlosDam'asio FabrizioRiguzzi EmmanuelDeMot RiccardoRosati YannisDimopoulos GiulianaSabbatini EsraErdem FaribaSadri WolfgangFaber ChiakiSakama DayaGaur FrancescoScarcello JensHappe TommiSyrjanen TomiJanhunen AndreaTettamanzi JoohyungLee BertVanNu?elen NicolaLeone HelmutVeith ThomasLinke GerardVreeswijk ThomasLukasiewicz KewenWang PaoloMancarella Jia-HuaiYou CristinelMateis DongmoZhang RobMiller Sponsoring Institutions We would like to acknowledge ?nancial support for the conference from the EuropeanO?ceofAerospaceResearchandDevelopment(EOARD),underc- tractF61775-01-WF077,theAustrianComputerSociety(OCG),theEuropean Commission,theAustrianMinistryofTransport,Innovation&Technology,and Microsoft. Table of Contents Invited Papers AComputationalLogicApproachtoHeterogenousAgentSystems ...1 JurgenDix DeclarativeInformationExtraction,WebCrawling, andRecursiveWrappingwithLixto ...21 RobertBaumgartner,SergioFlesca,andGeorgGottlob OntheComplexityofModelCheckingandInference inMinimalModels(ExtendedAbstract) ...42 LefterisM. KirousisandPhokionG. Kolaitis DataIntegrationNeedsReasoning ...54 MaurizioLenzerini NonmonotonicInductiveLogicProgramming ...62 ChiakiSakama Regular Papers StrongEquivalenceforLogicPrograms andDefaultTheories(MadeEasy)...81 HudsonTurner OntheE?ectofDefaultNegationontheExpressiveness ofDisjunctiveRules ...93 TomiJanhunen OntheExpressibilityofStableLogicProgramming ...107 V. W. MarekandJ. B. Remmel OntheRelationshipbetweenDefeasibleLogic andWell-FoundedSemantics ...121 GerhardBrewka AComparativeStudyofWell-FoundedSemantics forDisjunctiveLogicPrograms ...133 KewenWang ReasoningwithOpenLogicPrograms ...147 PieroA. Bonatti RepresentationofIncompleteKnowledgebyInduction ofDefaultTheories...