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From "Chuck Williams" <ch...@manawiz.com>
Subject RE: Normalized Scoring -- was RE: idf and explain(), was Re: Search and Scoring
Date Thu, 21 Oct 2004 21:18:00 GMT
That's what I get for reading code quickly that I haven't used.
Similarity.idf() calls MultiSearcher.docFreq() to compute the global
idf.  So since tf's, lengthNorm's and sloppyFreq's are document-local,
coord's and queryNorm's are properties of the query and the idf's, and
idf's are computed globally when searching multiple indices, I don't
know which problem Daniel is referring to by, "you currently cannot
search over several indices without getting an incorrect ranking (except
these indices were built from splitting one large index)".

Chuck

  > -----Original Message-----
  > From: Doug Cutting [mailto:cutting@apache.org]
  > Sent: Thursday, October 21, 2004 2:03 PM
  > To: Lucene Developers List
  > Subject: Re: Normalized Scoring -- was RE: idf and explain(), was
Re:
  > Search and Scoring
  > 
  > Chuck Williams wrote:
  > > However, I'm not sure this analysis is completely correct due to
  > MultiSearcher.docFreq() which appears to be trying to redefine the
tf's
  > to be the global value across all indices.  It wasn't clear to me
how
  > this code is ever reached, e.g. from TermQuery --> SegmentTermDocs.
If
  > the tf's and idf's are in fact computed globally, then the
interleaving
  > should work as it is, thus I'm guessing they are not.
  > 
  > Idf's are already computed globally across all indexes.  Tf's are
local
  > to the document.  In short, scores from a MultiSearcher are the same
as
  > when searching an IndexReader with the same documents.
  > 
  > Doug
  > 
  >
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