Problems with Rules-Based Systems

The greatest drawback to rules-based systems is the amount of time spent trying to match a rule with available working memory. Recall from the source discussion that there is not only the problem of one-to-one mapping of rules to working memory, but also variations based upon inexact terms. Therefore, instead of just trying to map a rule to working memory, we may have to perform multiple iterations over each rule. If a match is not found, the match process will continue through to each rule.

A solution to this problem exists, called the Rete algorithm [Forgy 1982]. The idea behind Rete is to share intermediate information between rules to limit the number of matches that must be performed. This is performed through an acyclic directed graph representing the antecedents for the rules. For example, if two rules share one common element of their antecedent, each rule would share a node within the graph for the comment element. From this node one would represent the remaining elements of their respective antecedents . In this way, a match for a given element is performed once, leading to possibly multiple rules that might match, but only computing the initial match once.