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    Optimizing sorting and duplicate elimination in xquery path expressions

    Hidders, Jan and Michiels, P. and Vercammen, R. (2005) Optimizing sorting and duplicate elimination in xquery path expressions. Bulletin of the European Association for Theoretical Computer Science 86 , pp. 199-223. ISSN 0252–9742.

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    The semantics of the standard XML query language XQuery requires that the results of its path expressions are in document order and duplicatefree. Many implementations of this semantics guarantee correctness by inserting explicit operations that sort and remove duplicates in their evaluation plans. The sorting and duplicate-removal operations are often either inserted after each step or only after the last step. However, both strategies have performance drawbacks. In this paper we show how to create more efficient evaluation plans by deciding statically where such operations are required. We present inference rules for deciding orderedness and duplicate-freeness of the results of evaluation plans and show that these rules are sound and, for certain evaluation plans, complete. These inference rules are implemented by an efficient, automaton-based algorithm. Experimental results show that the algorithm is effective on many common path expressions.


    Item Type: Article
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Computing and Mathematical Sciences
    Depositing User: Sarah Hall
    Date Deposited: 13 Apr 2021 15:45
    Last Modified: 09 Aug 2023 12:50


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