S3: Evaluation of Tree-Pattern Queries Supported by Structural Summaries

XML queries are frequently based on path expressions where their elements are connected to each other in a tree-pattern structure, called query tree pattern (QTP). Therefore, a key operation in XML query processing is finding those elements which match the given QTP. In this paper, we propose a novel method, called S^3, which can selectively process the document's nodes. In S^3, unlike all previous methods, path expressions are not directly executed on the XML document, but first they are evaluated against a guidance structure, called QueryGuide. Enriched by information extracted from the QueryGuide, a query execution plan, called SMP, is generated to provide focused pattern matching and avoid document access as far as possible. Moreover, our experimental results confirm that S^3 and its optimized version OS^3 substantially outperform previous QTP processing methods w.r.t. response time, I/O overhead, and memory consumption - critical parameters in any real multi-user environment.

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