A Frameworkfor Investigating Production System Formulations with Polynomially Bounded Match

Real time constraints on AI systems require guaranteeing bounds on these systems' performance. However, in the presence of sources of uncontrolled combinatorics, it is extremely difficult to guarantee such bounds on their performance. In production systems, the primary source of uncontrolled combinatorics is the production match. To eliminate these combinatorics, the unique-attribute formulation was introduced in (Tambe and Rosenbloom, 1989), which achieved a linear bound on the production match. This formulation leads to several questions: is this unique-attributes formulation the best conceivable production system formulation? In fact, are there other alternative production system formulations? If there are other formulations, how should these alternatives be compared with the unique-attribute formulation? This paper attempts to address these questions in the context of Soar. It identifies independent dimensions along which alternative production system formulations can be specified. These dimensions are based on the fixed class of match algorithms currently employed in production systems. These dimensions create a framework for systematically generating alternative formulations. Using this framework we show that the unique-attribute formulation is the best one within the dimensions investigated. However, if a new class of match algorithms is admitted, by relaxing certain constraints, other competitor formulations emerge. The paper indicates which competitor formulations are promising and why. Although some of the concepts, such as unique-attributes, are introduced in the context of Soar, they should also be relevant to other rule-based systems.