Preferred answer sets for extended logic programs
Artificial Intelligence
Expressing preferences in default logic
Artificial Intelligence
Nonmonotonic Logic: Context-Dependent Reasoning
Nonmonotonic Logic: Context-Dependent Reasoning
Intellectics and Computational Logic (to Wolfgang Bibel on the occasion of his 60th birthday)
Adding Priorities and Specificity to Default Logic
JELIA '94 Proceedings of the European Workshop on Logics in Artificial Intelligence
A semantic framework for preference handling in answer set programming
Theory and Practice of Logic Programming
On specificity in default logic
IJCAI'95 Proceedings of the 14th international joint conference on Artificial intelligence - Volume 2
Default reasoning with preference within only knowing logic
LPNMR'05 Proceedings of the 8th international conference on Logic Programming and Nonmonotonic Reasoning
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Practical use of default logics requires mechanisms to select the more suitable extensions from out of the several often allowed by a classical default theory. An obvious solution is to order defaults in a preference hierarchy, and use this ordering to select preferred extensions. The literature contains many suggestions on how to implement such a scheme. The problem is that they yield different results: all authors agree that preferred extensions employ preferred defaults, but this apparent agreement hides differences in lower level decisions. While motivations for these are rarely discussed, their consequences for overall behaviour are wide-ranging. This paper points towards standardisation, discussing principles that ought to hold and then working top-down to determine lower level details. We present characterisations, uncover anomalies of existing approaches, and suggest repairs. We build on work by Brewka and Eiter [4], who first identified some of the desiderata discussed here. A slightly modified version of the notion of preferred extension proposed by these authors, and one by Delgrande and Schaub [5], are identified as the most and least inclusive notions of extension satisfying all desiderata. We point out that these two (in the literature previously termed "descriptive" and "prescriptive", respectively) differ along two rather independent dimensions, and two additional notions are then identified, representing the remaining possibilities.