XWAVE: optimal and approximate extended wavelets

  • Authors:

  • Sudipto Guha;Chulyun Kim;Kyuseok Shim

  • Affiliations:

  • University of Pennsylvania;Seoul National University;Seoul National University

  • Venue:
  • VLDB '04 Proceedings of the Thirtieth international conference on Very large data bases - Volume 30
  • Year:
  • 2004

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Abstract

Wavelet synopses have been found to be of interest in query optimization and approximate query answering. Recently, extended wavelets were proposed by Deligiannakis and Roussopoulos for data sets containing multiple measures. Extended wavelets optimize the storage utilization by attempting to store the same wavelet coefficient across different measures. This reduces the bookkeeping overhead and more coefficients can be stored. An optimal algorithm for minimizing the error in representation and an approximation algorithm for the complementary problem was provided. However, both their algorithms take linear space. Synopsis structures are often used in environments where space is at a premium and the data arrives as a continuous stream which is too expensive to store. In this paper, we give algorithms for extended wavelets which are space sensitive, i.e., use space which is dependent on the size of the synopsis (and at most on the logarithm of the total data) and operates in a streaming fashion. We present better optimal algorithms based on dynamic programming and a near optimal approximate greedy algorithm. We also demonstrate the performance benefits of our algorithms compared to previous ones through experiments on real-life and synthetic data sets.