Dictionaries and Tolerant Retrieval

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Introduction to Information RetrievalB‐trees handle *’s at the end of aSec. 3.2query term• How can we handle*’s in the middle of query term?• co*tion• We could look up co* AND *tion in a B‐tree andintersect the two term sets• Expensive• The solution: transform wild‐card queries so that the*’s occur at the end• This gives rise to the Permuterm Index.14
Introduction to Information RetrievalSec. 3.2.1Permuterm index• For term hello, index under:• hello$, ello$h, llo$he, lo$hel, o$hellwhere $ is a special symbol.• Queries:• X lookup on X$ X* lookup on $X*• *X lookup on X$* *X* lookup on X*• X*Y lookup on Y$X* X*Y*Z ??? Exercise!Query = hel*oX=hel, Y=oLookup o$hel*15
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Dictionaries and Tolerant Retrieval

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