Managing Con icts between Rules

Rules are used as a programmingparadigm in several application domains, including active databases, planning, expert systems, and billing. For example, active databases have rules that execute upon the occurrence of particular events if speciied condition predicates are satissed. It is often the case that multiple rules are reable when a particular event occurs. We propose a declarative mechanism to control the interaction and execution of multiple rules. The mechanism is based upon logical metarules that can express various types of relationships between rules. The metarules allow us to reason statically about the rule behavior. We can determine, in polynomial time, if a rule will never execute, whether two rules can ever be executed together, and whether a rule system is guaranteed to have a unique execution set for all possible rules that become reable. In this paper, we illustrate our techniques using rules in an active database. A system based upon the metarules and the static analysis presented here has been found to be of value in a billing application at AT&T to control interactions between discount plans.