Maintaining significant stream statistics over sliding windows

  • Authors:
  • L. K. Lee;H. F. Ting

  • Affiliations:
  • The University of Hong Kong, Pokfulam, Hong Kong;The University of Hong Kong, Pokfulam, Hong Kong

  • Venue:
  • SODA '06 Proceedings of the seventeenth annual ACM-SIAM symposium on Discrete algorithm
  • Year:
  • 2006

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Abstract

In this paper, we introduce the Significant One Counting problem. Let ε and θ be respectively some user-specified error bound and threshold. The input of the problem is a stream of bits. We need to maintain some data structure that allows us to estimate the number of 1-bits in a sliding window of size n such that whenever there are at least θn 1-bits in the window, the relative error of the estimate is guaranteed to be at most ε. When θ 1/n, our problem becomes the Basic Counting problem proposed by Datar et al. [ACM-SIAM Symposium on Discrete Algorithms (2002), pp. 635--644]. We prove that any data structure for the Significant One Counting problem must use at least Ω(1/ε log2 1/θ + log ε θn) bits of memory. We also design a data structure for the problem that matches this memory bound and supports constant query and update time. Note that for fixed θ and ε, our data structure uses O(log n) bits of memory, while any data structure for the Basic Counting problem needs Ω(log2 n) bits in the worst case.