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From Chris Hostetter <>
Subject Re: sumOfSquaredWeights for lengthNorm
Date Mon, 06 Mar 2006 21:31:29 GMT

: I would like to override the Similarity class lengthNorm(String
: fieldName, int numTerms) so that it behaves similar to queryNorm(float
: sumOfSquaredWeights).  So the method signature becomes lengthNorm(String
: fieldName, float sumOfSquaredWeights) where sumOfSquaredWeights = sum of
: the squares of doc term weights.
: Looking at the way sumOfSquaredWeights was used in
: weight method, I would like to have a
: weight method in org.apache.lucene.document.Field (or may be in
: org.apache.lucene.document.Document) which returns the weight based on
: the terms in the Field. Can anyone tell me how to start?

can you explain more what you mean by "doc term weights" ?

It seems like what you are interested in doing is changing the way norm
value of a doc/field is determined so that it's determined not just by the
number of terms in the field, but also by the "weight" or some terms --
i'm not sure if you mean the terms being queried on, or the terms stored
in the field for the document

Two concepts that already exist (and may be useful to you) are:

1) the "boosts" associated with Fields and Documents at indexing time,
which are combined with the lengthNorm at index time to determine a single
"norm"  value for the doc/field pair.

2) the idf of the terms being queried on, which is multiplied by the field
norm as part of the query time scoring (you can see it in the
fieldWeight in a score Explanation)


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