1. Efficient Progressive Processing of Skyline Queries in Peer-to-Peer Systems INFOSCALE’06

2. Outline Introduction Algo Evaluation Conclusion

3. Introduction Finding a hotel with nearest distance to a beach and a lower price Distance Price

4. Semantic Small Word Peer Choose the centroid of its largest data cluster as its semantic label Each node in the network knows its local neighbors, called short range contacts. Each node knows a small number of randomly chosen nodes,called long range contacts Peer is responsible for management of data objects and the location information of data objects stored at other peers referred as foreign indexes

5. Cont. SSW Overlay Structure Foreign Indexes short long

6. Problem Definition For a 4-Dimension SSW {a0,a1,a2,a3} A Skyline Query={a0:min, a2:max} Q is only related to attribute dimension a0 and a2 only.

7. Algo. Exact Algo. Step: Locate the Origin Cluster Find the boundary value in the skyline query(v bound ) Inter-Cluster Pruning Forwarded to peers in neighboring cluster as long as the cluster is not dominated by v bound. Intra-Cluster Pruning prune irrelevant peers Skyline Computing

8. Exact Algo.

9. Approximate Algo.(Single-Path) In cases where a semantic overlay network does not exist. Receiving an incoming skyline query Q, the initial peer must decide the next candidate peer to which the skyline query is forwarded from its knowledge of contact Semantic Distance ： attribute of candidate peer ： attribute of current peer

10. Single-Path PriceDistance to Beach Current peer10166

11. Discussion and Improvement Consider A,B in the candidate list A is cheaper. B is near to the beach. Case: Choose A If B contains many hotel records that are near to the beach Therefore, an import portion of a good skyline is neglected

12. Multi-path Semantic Distance The score function return a j-tuple set instead of a single result

13. Cont. PriceDistance to Beach Current peer10166 Peer IDPriceDistance to BeachScore A7965-22,-1 B73 -28,7 C8859-13,-7 D1826581,-1 E103702,4 F6984-32,18 G9068-11,2 F,C will be selected.

14. Evaluation Result Quality Return the area between an approximate skyline with a complex exact one that takes all the data objects in the network in to consideration.

15. Cont.

16. Conclusion