Efficient XQuery Evaluation of Grouping Conditions with Duplicate Removals

  • Norman May
  • Guido Moerkotte
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4704)


Currently, grouping in XQuery must be expressed implicitly with nested FLWOR expressions. With XQuery 1.1, an explicit group by clause will be part of this query language. As users integrate this new construct into their applications, it becomes important to have efficient evaluation techniques available to process even complex grouping conditions. Among them, the removal of distinct values or distinct nodes in the partitions defined by the group by clause is not well-supported yet. The evaluation technique proposed in this paper is able to handle duplicate removal in the partitions efficiently. Experiments show the superiority of our solution compared to state-of-the-art query processing.


Query Processing Aggregate Function Partial Plan Aggregation Variable Query Execution Time 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Norman May
    • 1
  • Guido Moerkotte
    • 1
  1. 1.University of Mannheim, B6, 29, 68131 MannheimGermany

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