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lecture1-intro-handout-6-per

# Gthisslidehasdisnctlyidenedzonessuchas

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Unformatted text preview: orma)on Retrieval Sec. 1.3 Query op)miza)on example  More general op)miza)on    Process in order of increasing freq:    e.g., (madding OR crowd) AND (ignoble OR strife)    Get doc. freq.’s for all terms.    Es)mate the size of each OR by the sum of its  doc. freq.’s (conserva)ve).    Process in increasing order of OR sizes.    start with smallest set, then keep cuEng further.  This is why we kept document freq. in dictionary 2 Brutus Caesar Calpurnia 4 1 2 8 16 32 64 128 3 5 8 16 21 34 13 16 Execute the query as (Calpurnia AND Brutus) AND Caesar.  31  Introduc)on to Informa)on Retrieval 32  Introduc)on to Informa)on Retrieval Exercise  Query processing exercises    Exercise: If the query is friends AND romans AND (NOT countrymen), how could we use the freq of  countrymen?    Exercise: Extend the merge to an arbitrary Boolean  query.  Can we always guarantee execu)on in )me  linear in the total pos)ngs size?    Hint: Begin with the case of a Boolean formula query  where each term appears only once in the query.    Recommend a query  processing order for  (tangerine OR trees) AND (marmalade OR skies) AND (kaleidoscope OR eyes) 33  Introduc)...
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