Author Description

ThisvolumeconsistsoftherefereedpaperspresentedattheFifthInternational ConferenceonLogicProgrammingandNonmonotonicReasoning(LPNMR'99) heldatElPaso, Texas, inDecember1999. LPNMR'99isthe fthinaseriesofinternationalmeetingsonlogicprogramming andnonmonotonicreasoning. FourpreviousmeetingswereheldinWashington, U. S. A., in1991, inLisbon, Portugal, in1993, inLexington, U. S. A., in1995, and inDagstuhl, Germany, in1997. TheaimoftheLPNMRconferencesisto- cilitateinteractionsbetweenresearchersinterestedinlogicbasedprogramming languagesanddatabasesystemsandresearcherswhoworkintheareasofk- wledgerepresentationandnonmonotonicreasoning. Inadditiontopresentationsofacceptedpaperstheconferencewillfeaturetalks byfourinvitedspeakersMarcoCadoli, VladimirLifschitz, DavidMcAllester, andLeoraMorgenstern. ManypeoplecontributedtothesuccessoftheLPNMR'99conference. Special thanksareduetotheprogramcommitteeandtheadditionalreviewersforcareful evaluationofthesubmittedpapers. WewouldalsoliketothankGopalGuptaand DannyDeSchreyefortheire ortsincoordinatingtheschedulesofICLP99and LPNMR99, andGeorgGottlob, chairoftheLPNMRsteeringcommittee, who providedcontinuousadviseandsupporttotheprogramchairs. Theconference was nanciallysupportedbytheUniversityofTexasatElPasoandCompulog NetprovidedsupportforaEuropeaninvitedspeaker. December1999 MichaelGelfond NicolaLeone GeraldPfeifer ConferenceOrganization ProgramCo-Chairs MichaelGelfond(UniversityofTexasatElPaso, USA) NicolaLeone(ViennaUniversityofTechnology, Austria) ProgramCommittee JoseJulioAlferes(UniversidadedeEvora, Portugal) ChittaBaral(UniversityofTexasatElPaso, USA) NicoleBidoit(Universit edeBordeaux1, France) J]urgenDix(UniversityofKoblenz, Germany) ThomasEiter(ViennaUniversityofTechnology, Austria) FangzhenLin(TheHongKongUniversityofScienceandTechnology, China) JackMinker(UniversityofMaryland, USA) AnilNerode(CornellUniversity, USA) IlkkaNiemela(HelsinkiUniversityofTechnology, Finland) DinoPedreschi(UniversityofPisa, Italy) PasqualeRullo(UniversityofCal