CHAPTER 5 – Resolution Strategies

Publisher Summary This chapter describes the different aspects of resolution strategies. One of the disadvantages of using the resolution rule in an unconstrained manner is that it leads to many useless inferences. Some inferences are redundant in that their conclusions can be derived in other ways. Some inferences are irrelevant in that they do not lead to derivations of the desired result. A deletion strategy is a restriction technique in which clauses with specified properties are eliminated before they are ever used. As those clauses are unavailable for subsequent deduction, this can lead to computational savings. A literal occurring in a database is pure only if it has no instance that is complementary to an instance of another literal in the database. A clause that contains a pure literal is useless for the purposes of refutation as the literal can never be resolved away. One can safely remove such a clause. Removing clauses with pure literals defines a deletion strategy known as pure-literal elimination.