The Hyper System : Knowledge Reformation forE cient First - order

We present the Hyper system that implements a new approach to knowledge compilation, where function-free rst-order acyclic Horn theories are transformed to propositional logic. The compilation method integrates techniques from deductive databases (relevance reasoning) and theory transformation via unfold/fold transformations, to obtain a compact propositional representation. The transformed theory is more compact than the ground version of the original theory in terms of signiicantly less and mostly shorter clauses. This form of compilation, called knowledge (base) reformation, is important since the most eecient reasoning methods are deened for propositional theories, while knowledge is most naturally expressed in a rst-order language. In particular, we will show that knowledge reformation allows low-order polynomial time inference to nd a near-optimal solution in cost-based rst-order hypothetical reasoning (oràbduction') problems. We will also present experimental results that connrm the eeectiveness of our compilation method.