A SOURCE-TO-SOURCE TRANSFORMATION FOR INCREASING RULE-BASED SYSTEM PARALLELISM

Rule-based systems have been hypothesized to contain only minimal parallelism. However, techniques to extract more parallelism from existing systems are being investigated. Among these methods, it is desirable to find those which balance the work being performed in parallel evenly among the rules, while decreasing the amount of work being performed sequentially in each cycle. The automatic transformation of creating constrained copies of culprit rules accomplishes both of the above goals. Rule-based systems are plagued by occasional rules which slow down the entire execution. These culprit rules require much more processing than others, causing other processors to idle while they continue to match. By creating constrained copies of culprit rules and distributing them to their own processors, more parallelism is achieved, as evidenced by increased speed up. This effect is shown to be specific to rule-based systems with certain characteristics. These characteristics are identified as being common within an important class of rule-based systems: expert database systems.