Alternating Fixed Points in Boolean Equation Systems as Preferred Stable Models

13 years 9 months ago

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We formally characterize alternating ﬁxed points of boolean equation systems as models of (propositional) normal logic programs. To this end, we introduce the notion of a preferred stable model of a logic program, and deﬁne a mapping that associates a normal logic program with a boolean equation system such that the solution to the equation system can be “read oﬀ” the preferred stable model of the logic program. We also show that the preferred model cannot be calculated a-posteriori (i.e. compute stable models and choose the preferred one) but rather must be computed in an intertwined fashion with the stable model itself. The mapping reveals a natural relationship between the evaluation of alternating ﬁxed points in boolean equation systems and the GelfondLifschitz transformation used in stable-model computation. For alternation-free boolean equation systems, we show that the logic programs we derive are stratiﬁed, while for formulas with alternation, the corresponding pr...

K. Narayan Kumar, C. R. Ramakrishnan, Scott A. Smo

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