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9 Algorithms: PageRank

9 Algorithms: PageRank. Ranking. After matching, have to rank:. Index Based Ranking. Strategies we could (do) use: Frequency Position Metadata. Missing Ingredient. Index lacks intra-page information. Link Quality. More links is easy to abuse. Spam Link Pages. Link Quality.

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9 Algorithms: PageRank

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  1. 9 Algorithms:PageRank

  2. Ranking • After matching, have to rank:

  3. Index Based Ranking • Strategies we could (do) use: • Frequency • Position • Metadata

  4. Missing Ingredient • Index lacks intra-page information

  5. Link Quality • More links is easy to abuse Spam Link Pages

  6. Link Quality • Not all links are equal • Who do you trust? • CS Prof • World Famous Chef

  7. Identifying Authority • Links into a page give it authority • Page value = sum of authorities of pages linking to it

  8. Issues • Spam Links • Discourage with negative weight Spam Link Pages -1 -1 -1 -1 -1 -1

  9. Issues • Spam Links • Discourage with negative weight • Cycles:

  10. Issues • Spam Links • Discourage with negative weight • Cycles:

  11. Issues • Spam Links • Discourage with negative weight • Cycles: …

  12. Random Surfer • Simulating a web surfing session • Start at random page • At each page have a chance to • Pick a random link to go to • Jump to a completely random page

  13. Results • Results of many random sessions:

  14. Results • Expressed as percentages, results stabilize • Law of large numbers

  15. Cycle Buster • Random surfer not phased by cycles:

  16. Random Surfer In Use • The recipe pages visited by random surfers:

  17. Simulator • PageRank Simulator: http://caccio.blogdns.net/software/pagerank-simulator

  18. The Real Math • Markov Chains • Set of states • Each state has probability of leading to other states • Represent as matrix

  19. Excel Simulation • Three pages:

  20. Limitations • Still have issues/room for growth • Link Spam • Context of link • Where link is on page • "Bob's recipe is terrible" vs "Bob's recipe is great" • Lack of semantic knowledge • Page's Authority should not be the same for all domains

  21. Power • Controlling search is power: http://www.bitsbook.com/ "If you're not paying for the product, you are the product."

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