Negation as failure and constraints through abduction and defaults
The paper presents an extension of the abduction framework proposed by Eshghi and Kowalski to give the semantics of negation as failure in logic programming. The extension allows to cope with the presence of integrity constraints, not only for pruning inconsistent solutions, but for computing new solutions. This is achieved by adding constraints to the program and using them as logical formulae. Furthermore a new semantics based on defaults, equivalent to the previous one, is given for logic programs with negation as failure and constraints. Finally a transformation is presented which allows constraints to be eliminated, so that proof procedures for general clauses without constraints will be applicable.
The approach proposed in this paper is applicable not only to logic programs with negation as failure but to other nonmonotonic formalisms as well, and, for instance, it can be used to give a semantic characterization to justificationbased Truth Maintenance Systems with dependency-directed backtracking.
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