Counting Distinct Objects over Sliding Windows
Wenjie Zhang, Ying Zhang, Muhammad Aamir Cheema, Xuemin Lin · 2010
Aggregation against distinct objects has been in-volved in many real applications with the presence of duplicates, including real-time monitoring mov-ing objects. In this paper, we investigate the prob-lem of counting distinct objects over sliding windows with arbitrary lengths. We present novel, time and space efficient, one scan algorithms to continuously maintain a sketch so that the counting can be ap-proximately conducted with a relative error guaran-tee ǫ in the presence of object duplicates. Efficient query algorithms have also been developed by ef-fectively utilizing the skyband property. Moreover, the proposed techniques may be immediately applied to the range counting aggregation and heavy hitter problem against distinct elements. A comprehensive performance study demonstrates that our algorithms can support real-time computation against high speed data streams. 1