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Justifications for programs with disjunctive and causal-choice rules*

Published online by Cambridge University Press:  14 October 2016

PEDRO CABALAR
Affiliation:
Department of Computer Science, University of Corunna, Corunna, Spain (email: cabalar@udc.es, jorge.fandino@udc.es)
JORGE FANDINNO
Affiliation:
Department of Computer Science, University of Corunna, Corunna, Spain (email: cabalar@udc.es, jorge.fandino@udc.es)

Abstract

In this paper, we study an extension of the stable model semantics for disjunctive logic programs where each true atom in a model is associated with an algebraic expression (in terms of rule labels) that represents its justifications. As in our previous work for non-disjunctive programs, these justifications are obtained in a purely semantic way, by algebraic operations (product, addition and application) on a lattice of causal values. Our new definition extends the concept of causal stable model to disjunctive logic programs and satisfies that each (standard) stable model corresponds to a disjoint class of causal stable models sharing the same truth assignments, but possibly varying the obtained explanations. We provide a pair of illustrative examples showing the behaviour of the new semantics and discuss the need of introducing a new type of rule, which we call causal-choice. This type of rule intuitively captures the idea of “A may cause B” and, when causal information is disregarded, amounts to a usual choice rule under the standard stable model semantics.

Type
Regular Papers
Copyright
Copyright © Cambridge University Press 2016 

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Footnotes

*

This research was partially supported by Spanish Project TIN2013-42149-P.

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