www-ai.cs.tu-dortmund.de/LEHRE/FACHPROJEKT/SS12/paper/counting/Arasu2004.pdf
sequence of bags for a variable-size window over this stream is the following: {15}, {15, 7}, {7}, {7, 6}, {7, 6, 24}, {7, 6, 24, 21}, {6, 24, 21}, . . .. 2
Fixed- and variable-size sliding windows abstract [...] Consider the stream 15, 7, 6, 24, 21, 24, . . .. A fixed-size sliding window over this stream with size N = 3 produces the following sequence of bags: {15}, {15, 7}, {15, 7, 6}, {7, 6, 24}, {6, 24, 21}, [...] that requires only O( 1
ε log(εδ)−1) space, beating the
sampling bound. Cormode and Muthukrishnan [7] recently presented randomized algorithms for identifying frequency counts in the presence of both additions …