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From Paul Elschot <>
Subject Re: clarification on booleanScorer
Date Tue, 03 Jul 2007 06:56:35 GMT

On there is normally a higher chance of
getting a response.

You may have missed this:

Your analysis below is correct, only a few points need to be added:
- the coordination factor, which favours more matching clauses
  (for prefix queries normally no coordination is used),
- your examples are nested boolean queries, so all this applies on
  each level, and
- the idf computation is a bit more involved, see the reference above.

Paul Elschot

On Tuesday 03 July 2007 01:38, #MAGGY ANASTASIA SURYANTO# wrote:
> Hi all,
> I would like to clarify my understanding of the way Lucene score boolean 
queries, in relation with +/  clause attributes (required and optional) as 
well as OR and AND operators. 
> After looking at the BooleanScorer source core, the following is my 
understanding on the scoring:
> 1. OR is translated into " " (optional) and AND is translated into 
"+" (required) by queryParser
>  so, is it true that 
> (t1 t2 t3) AND (t4 t5 t6)  OR  (t7 t8 t9)  is parsed by queryParser into the 
following boolan query
> +(t1 t2 t3) +(t4 t5 t6) (t7 t8 t9)
> 2. using default similarity, a score of a document score(q,d) is the 
summation of the tf, idf measure of the terms in q that appear in d. 
> 3. Score of a document w.r.t BooleanClause, BC (score(BC,d)) is the sum of 
score of the document w.r.t sall sub clauses of BC.
> 4. no difference in treating "+" clauses and " " clauses in scoring (i.e. 
their scorer.score() are summed up together to produce the total score of 
their parent' score), however, the addition of the scores of " " clauses are 
delayed until all "+" are matched by the documents. If not all "+" mare 
matched, the document is not retrieved.
>          -----C1-----    ----C2-----    ----C3-----      ------C4-------
> q = +{+(t1 t2 t3)   +(t4 t5 t6)   (t7 t8 t9)}     {t10 t11 t12}
> assuming a document,d  match C1 and C2, the s(q,d) = sum(sum(s(C1,d) + 
s(C2,d) + s(C3, d)), s(C4,d))
> Please let me know whether the above are true. In case there are something I 
miss to understand the scoring of booleanScorer, please let me know.
> best regards
> maggy

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