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Abstract

We define \emph{order locality} to be a property of clauses relative to a term ordering. This property is a generalization of the subformula property for proofs where terms arising in proofs are bounded, under the given ordering, by terms appearing in the goal clause. We show that when a clause set is order local, then the complexity of its ground entailment problem is a function of its structure (e.g., full versus Horn clauses), and the ordering used. We prove that, in many cases, order locality is equivalent to a clause set being saturated under ordered resolution. This provides a means of using standard resolution theorem provers for testing order locality and transforming non-local clause sets into local ones. We have used the Saturate system to automatically establish complexity bounds for a number of nontrivial entailment problems relative to complexity classes which include Polynomial and Exponential Time and co-NP.