Kyriakos Mouratidis, Spiridon Bakiras, Dimitris Papadias SIGMOD 2006 1

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Continuous Monitoring of Top-k Queries over SlidingWindows

Kyriakos Mouratidis, Spiridon Bakiras, Dimitris Papadias

SIGMOD 2006

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Motivation

Preliminaries

Method◦ TMA(Top-k Monitoring Algorithm)◦ SMA(Skyband Monitoring Algorithm)

Experimental evaluation

Conclusion

Outline

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The existing methods are inapplicable to highly dynamic environments involving numerous longrunning queries.

This paper studies continuous monitoring of top-k queries over a fixed-size window W of the most recent data.

Motivation

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f(X1,X2)=X1+2*X2

Preliminaries

(0.2,1)

(1,0.7)

(0.6,0.8)

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Cont.K-skyband :Returns those objects that are dominated by at most K-1 other objects.

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TMA(Top-k Monitoring Algorithm)

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f(X1,X2)=X1+2*X2

Top-1

Computation Module

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F(X1,X2)=X1-X2

Top-2

Cont.

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P1,P2 expire P3,P4 arriveSearch influence list-> P3 has maxscoreP3 become the result of top-1 query

Maintenance Module

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P3 expire P5 arrive invokes the top-k computation module

Cont.

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SMA applies the reduction from top-k to k-skyband queries in order to avoid computation from scratch when some results expire.

SMA(Skyband Monitoring Algorithm)

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DC(dominance counter)

2-skybandWhen DC reach 2,then delete.

Cont.

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P9 arrive

Cont.

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P9 arrive

Cont.

(2)

(1)

(2)

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P9 arrive

Cont.

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SMA is expected to be faster than TMA, since it involves less frequent calls to the top-k computation module.

Cont.

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Experimental evaluation

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TMA re-computes the result from scratch, whereas SMA maintains a superset of the current answer in the form of a k-skyband, in order to avoid frequent recomputations.

Conclusion