Efficient Evaluation of NOT-Twig Queries in Tree-Unaware Relational Databases

Abstract

Despite a large body of work on xml query processing in relational environment, systematic study of not-twig queries has received little attention in the literature. Such queries contain not-predicates and are useful for many real-world applications. In this paper, we present an efficient strategy to evaluate not-twig queries on top of a dewey-based tree-unaware system called Sucxent++ [11]. We extend the encoding scheme of Sucxent++ by adding two new labels, namely AncestorValue and AncestorDeweyGroup, that enable us to directly filter out elements satisfying a not-predicate by comparing their ancestor group identifiers. In this approach, a set of elements under the same common ancestor at a specific level in the xml tree is assigned same ancestor group identifier. Based on this encoding scheme, we propose a novel sql translation algorithm for not-twig query evaluation. Real and synthetic datasets are employed to demonstrate the superiority of our approach over industrialstrength rdbms and native xml databases