Improving the accuracy of histograms for geographic data objects

Abstract

Histograms have been widely used for estimating selectivity in query optimization. In this paper, we propose a new technique to improve the accuracy of histograms for two-dimensional geographic data objects that are used in many real-world applications. Typically, a histogram consists of a collection of rectangular regions, called buckets. The main idea of our technique is to use a straight line to convert each rectangular bucket to a new one with two separating regions. The converted buckets, called bichromatic buckets, can approximate the distribution of data objects better while preserving the simplicity of originally rectangular ones. To construct bichromatic buckets, we propose an algorithm to find good separating lines. We also describe how to apply the proposed technique to existing histogram construction methods to improve the accuracy of the constructed histograms. Results from extensive experiments using real-life data sets demonstrate that our technique improves the accuracy of the histograms by 2 times on average. © 2012 Springer-Verlag.