cs345-streams4

cs345-streams4 - 1 Stream Clustering Extension of DGIM to...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 Stream Clustering Extension of DGIM to More Complex Problems 2 Clustering a Stream ◆ Assume points enter in a stream. ◆ Maintain a sliding window of points. ◆ Queries ask for clusters of points within some suffix of the window. ◆ Important issue : where are the cluster centroids? 3 BDMO Approach ◆ BDMO = Babcock, Datar, Motwani, O’Callaghan. ◆ k –means based. ◆ Can use less than O( N ) space for windows of size N . ◆ Generalizes trick of DGIM: buckets of increasing “weight.” 4 Recall DGIM ◆ Maintains a sequence of buckets B 1 , B 2 , … ◆ Buckets have timestamps (most recent stream element in bucket). ◆ Sizes of buckets nondecreasing. ◗ In DGIM size = power of 2. ◆ Either 1 or 2 of each size. 5 Alternative Combining Rule ◆ Instead of “combine the 2 nd and 3 rd of any one size” we could say: ◆ “Combine B i+1 and B i if size(B i+1 ∪ B i ) < size(B i-1 ∪ B i-2 ∪ … ∪ B 1 ).” ◗ If B i+1 , B i , and B i-1 are the same size, inequality must hold (almost). ◗ If B i-1 is smaller, it cannot hold. 6 Buckets for Clustering ◆ In place of “size” (number of 1’s) we use (an approximation to) the sum of the distances from all points to the centroid of their cluster. of their cluster....
View Full Document

This document was uploaded on 03/04/2012.

Page1 / 21

cs345-streams4 - 1 Stream Clustering Extension of DGIM to...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online