Maximizing Top-down Constraints for Unification-based Systems

A left-corner parsing algorithm with top-down filtering has been reported to show very efficient performance for unification-based systems. However, due to the nontermination of parsing with left-recursive grammars, top-down constraints must be weakened. In this paper, a general method of maximizing top-down constraints is proposed. The method provides a procedure to dynamically compute *restrictor*, a minimum set of features involved in an infinite loop for every propagation path; thus top-down constraints are maximally propagated.