Using Prefix-Trees for Efficiently Computing Set Joins

Joins on set-valued attributes (set joins) have numerous database applications. In this paper we propose PRETTI (PREfix Tree based seT joIn) – a suite of set join algorithms for containment, overlap and equality join predicates. Our algorithms use prefix trees and inverted indices. These structures are constructed on-the-fly if they are not already precomputed. This feature makes our algorithms usable for relations without indices and when joining intermediate results during join queries with more than two relations. Another feature of our algorithms is that results are output continuously during their execution and not just at the end. Experiments on real life datasets show that the total execution time of our algorithms is significantly less than that of previous approaches, even when the indices required by our algorithms are not precomputed.