Abstract: A rules-based system makes use of a specification that is similar to those used in earlier systems, such as in OPS5, but does not require the computational complexity of implementations such as Rete. In some such implementations, matching of the applicable rules given a set of facts is simplified by providing preallocated storage locations for the Boolean values of the condition elements for each rule. The Boolean values are set by direct processing of each of the facts. These preallocated storage locations are arranged to allow efficient evaluation of the overall condition of each of the rules in a manner that is significantly more efficient than implementations of earlier rule-based systems.