Evaluation of top-k OLAP queries using aggregate r–trees

  • Authors:
  • Nikos Mamoulis;Spiridon Bakiras;Panos Kalnis

  • Affiliations:
  • Department of Computer Science, University of Hong Kong, Hong Kong;Department of Computer Science, Hong Kong University of Science and Technology, Hong Kong;Department of Computer Science, National University of Singapore

  • Venue:
  • SSTD'05 Proceedings of the 9th international conference on Advances in Spatial and Temporal Databases
  • Year:
  • 2005

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Abstract

A top-k OLAP query groups measures with respect to some abstraction level of interesting dimensions and selects the k groups with the highest aggregate value. An example of such a query is “find the 10 combinations of product-type and month with the largest sum of sales”. Such queries may also be applied in a spatial database context, where objects are augmented with some measures that must be aggregated according to a spatial division. For instance, consider a map of objects (e.g., restaurants), where each object carries some non-spatial measure (e.g., the number of customers served during the last month). Given a partitioning of the space into regions (e.g., by a regular grid), the goal is to find the regions with the highest number of served customers. A straightforward method to evaluate a top-k OLAP query is to compute the aggregate value for each group and then select the groups with the highest aggregates. In this paper, we study the integration of the top-k operator with the aggregate query processing module. For this, we make use of spatial indexes, augmented with aggregate information, like the aggregate R–tree. We device a branch-and-bound algorithm that accesses a minimal number of tree nodes in order to compute the top-k groups. The efficiency of our approach is demonstrated by experimentation.