
22 Knowledge Discovery from Data Streams
• Step 3
s
3
= ((24 + 11)/4)/2, d
3
= {((24 − 11)/4)/2}
s
3
= 4.375, d
3
= {1.625}
The sequence {4.375, 1.625, −2.5, −2.75, −1.5, −.5, 1.5, −1} are the coefficients
of the expansion. The process consists of adding/subtracting pairs of numbers,
divided by the normalization factor.
Wavelet analysis is popular in several streaming applications, because most
signals can be represented using a small set of coefficients. Matias et al. (1998)
present an efficient algorithm based on multi-resolution wavelet decomposition
for building histograms with application to database problems, like selectivity
estimation. In the same research