Applying cosine series to XML structural join size estimation

Abstract

As XML has become the de facto standard for data presentation and exchanging on the Web, XML query optimization has emerged as an important research issue. It is widely accepted that structural joins, which evaluate the containment (ancestor-descendant) relationships between XML elements, are important to the XML query processing. Estimating structural join size accurately and quickly thus becomes crucial to the success of XML query plan selection. In this paper, we propose to apply Cosine transform to structural join size estimation. Our approach captures structural information of XML data using mathematical functions, which are then approximated by the Cosine series. We derive a simple formula to estimate the structural join size using the Cosine series. Theoretical analyses and extensive experiments have been performed. The experimental results show that, compared with state-of-the-art IM-DA-Est method, our method is several order faster, requires less memory, and yields better or comparable estimates. © Springer-Verlag Berlin Heidelberg 2006.