01362nas a2200145 4500008004100000245007200041210006900113260009900182300000900281520082400290100002001114700002501134700002001159856003701179 2007 eng d00aTowards Tractable Local Closed World Reasoning for the Semantic Web0 aTowards Tractable Local Closed World Reasoning for the Semantic aGuimaraes, Portugalb13th Portuguese Conference on Aritficial Intelligence, EPIA 2007c12/2007 a3-143 aRecently, the logics of minimal knowledge and negation as failure MKNF [12] was used to introduce hybrid MKNF knowledge bases [14], a powerful formalism for combining open and closed world reasoning for the Semantic Web. We present an extension based on a new three-valued framework including an alternating fixpoint, the well-founded MKNF model. This approach, the well-founded MKNF semantics, derives its name from the very close relation to the corresponding semantics known from logic programming. We show that the well-founded MKNF model is the least model among all (three-valued) MKNF models, thus soundly approximating also the two-valued MKNF models from [14]. Furthermore, its computation yields better complexity results (up to polynomial) than the original semantics where models usually have to be guessed.1 aKnorr, Matthias1 aAlferes, Jose, Julio1 aHitzler, Pascal uhttp://www.knoesis.org/node/1263