Computing Default Extensions by Reductions on $O^R$

Espen H. Lian, Arild Waaler

Based on a set of simple logical equivalences we define a rewriting procedure that computes extensions in the propositional fragment of the logic of OR introduced by Lakemeyer and Levesque. This logic is capable of representing default logic with the advantage of itself being monotonic, with a clearly defined semantics and a separation of the object level and the meta level. The procedure prepares the ground for efficient implementations as it clearly separates the SAT-solving part of the reasoning problem from the modal aspects that are specifically caused by defaults. We sketch an extension of the logic to cover confidence levels and show that the resulting system can accommodate ordered default theories with a prescriptive interpretation of preference between defaults.


Subjects: 3.3 Nonmonotonic Reasoning; 11. Knowledge Representation

Submitted: Jun 16, 2008

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