Using Delta Relations to Optimize Condition Evaluation in Active Databases

Abstract

We give a method for improving the effciency of condition evaluation during rule processing in active database systems. The method derives, from a rule condition, two improved conditions that can be used in place of the original condition when a previous value (true or false) of the original condition is known. The derived conditions are more effcient the original condition because they replace references to entire database relations by references to delta relations, which typically are much smaller. Delta relations are accessible to rule conditions in almost all current active database systems, making this optimization broadly applicable. We specify an implementation of our rewriting method based on attribute grammars.