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PIVOTAL LABS
Standup – 1/30/2008

Help!

  • Does anybody know anything about Lucene scoring using a document boost?

    We see an exponential relationship between document boost and the fieldNorm component of the score for each term. Can anybody explain this?

Comments
  1. Rupert Fiasco says:

    Ask someone on the Lucene mailing list, or maybe on the Acts As Solr mailing list (if you’re acts_as_solr)

    http://groups.google.com/group/acts_as_solr

  2. Not sure what you mean by exponential. Some examples would help.
    If you need help, either consult Lucene ML or http://sematext.com/

  3. Mike Grafton says:

    I’ll give an example below, but for the record we solved this by upgrading our version of Lucene (we’re now using 2.1, which is what SOLR 1.2 uses).

    Here’s a little table the shows the relationship we saw between the document boost and the ‘fieldNorm’ component of the score contributed by one of the query terms that hit:

    boost  fieldNorm
    1.0    0.3125    =  (5/16, 2^-1.678)
    2.0    20.0      =  (2^4.3219, 2^1 * 10)
    3.0    256.0     =  (2^8)
    4.0    1280.0    =  (2^10.3219, 2^7 * 10)
    5.0    5120.0    =  (2^12.3219, 2^9 * 10)
    6.0    16384.0   =  (2^14.0)
    7.0    40960.0   =  (2^15.3219, 2^12 * 10)
    8.0    81920.0   =  (2^16.3219, 2^13 * 10)
    10.0   327680.0  =  (2^18.3219, 2^15 * 10)
    

    With the newer code we see a linear relationship.

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