The Space Complexity of Processing XML Twig Queries Over Indexed Documents

Abstract-- Current twig join algorithms incur high memory costs on queries that involve child-axis nodes. In this paper we provide an analytical explanation for this phenomenon. In a first large-scale study of the space complexity of evaluating XPath queries over indexed XML documents we show the space to depend on three factors: (1) whether the query is a path or a tree; (2) the types of axes occurring in the query and their occurrence pattern; and (3) the mode of query evaluation (filtering, full-fledged, or "pattern matching"). Our lower bounds imply that evaluation of a large class of queries that have child-axis nodes indeed requires large space. Our study also reveals that on some queries there is a large gap between the space needed for pattern matching and the space needed for full-fledged evaluation or filtering. This implies that many existing twig join algorithms, which work in the pattern matching mode, incur significant space overhead. We present a new twig join ...

• Type: Conference
• Year: 2008
• Where: ICDE
• Authors: Mirit Shalem, Ziv Bar-Yossef
• Keywords: Database, ICDE 2008, Incur Significant Space, Pattern Matching, Twig Join Algorithms