Twig'n Join: Progressive Query Processing of Multiple XML Streams
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Date
2007-09-03T08:58:02Z
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Abstract
We propose a practical approach to the progressive processing of (FWR) XQuery queries on multiple XML streams, called Twig.n Join (or TnJ). The query is decomposed into a query plan combining several Twig queries on the individual streams, followed by a join and a final Twig query. The processing is itself accordingly decomposed into three pipelined stages progressively producing streams of XML fragments. We use the recently proposed TwigM algorithm for the progressive evaluation of Twig queries. We devise an original progressive join algorithm for the XML fragments leveraging our previous work on relational result-rate based progressive joins. In addition, we propose a multi-way XML value join algorithm, which uses a result-oriented approach to determine the probing sequence for multiple XML streams. We comparatively evaluate the performance of the Twig.n Join variants using both synthetic and real-life data from standard XML query processing benchmarks. We show that Twig.n Join with a result-rate based approach is most effective and efficient.