Estimating Answer Sizes for XML Queries

Abstract. Estimating the sizes of query results, and intermediate results, is crucial to many aspects of query processing. In particular, it is necessary for effective query optimization. Even at the user level, predictions of the total result size can be valuable in "next-step" decisions, such as query refinement. This paper proposes a technique to obtain query result size estimates effectively in an XML database. Queries in XML frequently specify structural patterns, requiring specific relationships between selected elements. Whereas traditional techniques can estimate the number of nodes (XML elements) that will satisfy a node-specific predicate in the query pattern, such estimates cannot easily be combined to provide estimates for the entire query pattern, since element occurrences are expected to have high correlation. We propose a solution based on a novel histogram encoding of element occurrence position. With such position histograms, we are able to obtain estimates o...

• Type: Conference
• Year: 2002
• Where: EDBT
• Authors: Yuqing Wu, Jignesh M. Patel, H. V. Jagadish
• Keywords: Alternative Query Plans, Database, EDBT 2002, Effective Query Optimization, Entire Query Pattern