Distributed Rule Monitoring in Active Databases and Its Performance Analysis

Monitoring rules in a distributed active database involves three design issues: how to decompose rules, how to distribute rules to sites, and how to evaluate distributed rules correctly. In this paper, we study these three issues for complicated rules, which are complex and time-consuming to evaluate. We propose a new relational operator, AND, and the associated algebraic manipulations of this operator to nd independent parts of rule query, which can be distributed among sites. Due to problems introduced by geographical distribution of sites in a distributed system, such as communication delay and lack of a global clock, correct evaluation of distributed rules is not an easy task. We propose a distributed evaluation algorithm which guarantees the correctness of the evaluation result of the distributed rule by collecting consistent local results from sites to form the global view. The message count and the response time of this distributed evaluation algorithm are analyzed for triggering updates.