Computing Facts in Non-Horn Deductive Systems

Let S be a set of clauses (non-Horn as well as Horn ones), and q an atomic query. Consider the prob- lem of deriving from S all ground unit clauses satisfying q , which we call computing all facts for q . It is shown how a non-Horn system S can be transformed into a set of singleton -head -rules , SH (S) , such that computing of all facts for a given query q in S is reduced to the query evaluation in a set of Horn clauses relevant to q which is a SL $set of SH (S) . The transformation is sound and com- plete.

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