Optimizing Existential Datalog Queries

Abstract

The problem of pushing projections in recursive rules has received little attention The objective of this paper is to motivate this problem and present some (partial) solutions We consider programs with function-free rules, also known as Datalog programs After formally denning existential subquenes, we present a syntactic criterion for detecting them and then consider optimization in three areas 1) We identify the existential subquenes and make them explicit by rewntmg the rules This, in effect, automatically captures some aspects of Prolog's cut operator that are appropriate to the bottom-up model of computation 2) We eliminate argument positions in recursive rules by "pushing projections"3) We observe that "pushing projections"in rules also has the effect of making some rules (even recursive rules) redundant and try to (identify and) discard them.