IR-part1

Perhaps the simplest model to build an ir system on

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Unformatted text preview: c. 1.3 Query processing: AND §༊  Consider processing the query: Brutus AND Caesar §༊  Locate Brutus in the Dic*onary; §༊  Retrieve its pos*ngs. §༊  Locate Caesar in the Dic*onary; §༊  Retrieve its pos*ngs. §༊  “Merge” the two pos*ngs (intersect the document sets): 2 4 8 16 1 2 3 5 32 8 64 13 128 21 Brutus 34 Caesar 30 Introduc)on to Informa)on Retrieval S ec. 1.3 The merge §༊  Walk through the two pos*ngs simultaneously, in *me linear in the total number of pos*ngs entries 2 4 8 16 1 2 3 5 32 8 13 Brutus 34 Caesar 128 64 21 If the list lengths are x and y, the merge takes O(x+y) operations. Crucial: postings sorted by docID. 31 Introduc)on to Informa)on Retrieval S ec. 1.3 The merge §༊  Walk through the two pos*ngs simultaneously, in *me linear in the total number of pos*ngs entries 2 8 2 4 8 16 1 2 3...
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This document was uploaded on 02/14/2014.

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