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Information Retrieval 27

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Information Retrieval

27 June 2016

Ex 1 [points 3+3] Consider the Consistent Hashing technique

1. simulate its execution over the urls_ID = {1, 2, 4, 6, 7, 8, 11, 13} and the crawler_ID = {2,4,7}, by defining the hash function h(x) = 3*x mod 11.

2. Show what happens if the crawler_ID 2 faults.

Ex 2 [points 3+3+3]

 Construct a 2-gram index for the set of strings S={bat, baz, bit, box, zox}.

 Design an algorithm that finds all strings of S at 1-edit distance from P[1,p].

 Simulate the proposed algorithm over the string P=bix.

Ex 3 [ranks 4+4] Given the list of integers S=(2,4,8,10,13,14,15,21).

 Show how to compress it via Elias-Fano coding.

 Describe how to select the 5th integer from S, by assuming to have a Select_1 data structure over the array H.

Ex 4 [ranks 5+2]Given a graph G=(V,E),

Define the formulas of PageRank and its variant Personalized Page Rank (PPR), and comment on their interpretation.

Show how PPR is used to compute CoSimRank(u,v) for every pair of nodes u,v in the graph G.

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