Efficient evaluation of nearest common ancestor in XML twig queries using tree-unaware RDBMS

Abstract

Finding all occurrences of a twig pattern in a database is a core operation in XML query processing. Recent study showed that tree-aware relational framework significantly outperform tree-unaware approaches in evaluating structural relationships in XML twig queries. In this paper, we present an efficient strategy to evaluate a specific class of structural relationship called NCA-twiglet in a tree-unaware relational environment. Informally, NCA-twiglet is a subtree in a twig pattern where all nodes have the same nearest common ancestor (the root of NCA-twiglet). We focus on NCA-twiglets having parent-child relationships. Our scheme is build on top of our SUCXENT++ system. We show that by exploiting the encoding scheme of S UCXENT++ we can reduce useless structural comparisons in order to evaluate NCA-twiglets. Through a comprehensive experiment, we show that our approach is not only more scalable but also performs better than a representative tree-unaware approach on all benchmark queries with the highest observed gain factors being 352. © Springer-Verlag Berlin Heidelberg 2007.