Ordered Backward XPath Axis Processing against XML Streams

Authors:
Abdul Nizar M.;P. Sreenivasa Kumar
Affiliations:
Dept. of Computer Science and Engineering, Indian Institute of Technology Madras, Chennai, India 600 036;Dept. of Computer Science and Engineering, Indian Institute of Technology Madras, Chennai, India 600 036
Venue:
XSym '09 Proceedings of the 6th International XML Database Symposium on Database and XML Technologies
Year:
2009

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Abstract

Processing of backward XPath axes against XML streams is challenging for two reasons: (i) Data is not cached for future access. (ii) Query contains steps specifying navigation to the data that already passed by. While there are some attempts to process parent and ancestor axes, there are very few proposals to process ordered backward axes namely, preceding and preceding-sibling . For ordered backward axis processing, the algorithm, in addition to overcoming the limitations on data availability, has to take care of ordering constraints imposed by these axes. In this paper, we show how backward ordered axes can be effectively represented using forward constraints. We then discuss an algorithm for XML stream processing of XPath expressions containing ordered backward axes. The algorithm uses a layered cache structure to systematically accumulate query results. Our experiments show that the new algorithm gains remarkable speed up over the existing algorithm without compromising on bufferspace requirement.