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From "Radhalakshmi Sreedharan" <Radhalakshm...@infosys.com>
Subject RE: Need help : SpanNearQuery
Date Fri, 17 Apr 2009 07:07:10 GMT
Hi Steven,
Thanks for your reply.

I tried out your approach and the problem got solved to an extent but still it remains.

The problem is the score reduces quite a bit even now as bc is not found in the combinations
 ( bc,cd) ( bc,ef) and ( ab,bc,cd,ef) etc. 

The boosting infact has a negative impact and reduces the score further :(

The factor which is affected by boosting is the queryNorm .

With a boost of 6  - 

0.015559823 = (MATCH) max of:
  0.015559823 = (MATCH) weight(spanNear([SearchField:cd, SearchField:ef], 10, false)^6.0 in
0), product of:
    0.07606166 = queryWeight(spanNear([SearchField:cd, SearchField:ef], 10, false)^6.0), product
of:
      6.0 = boost
      0.61370564 = idf(SearchField: cd=1 ef=1)
      0.02065639 = queryNorm
    0.20456855 = (MATCH) fieldWeight(SearchField:spanNear([cd, ef], 10, false)^6.0 in 0),
product of:
      0.33333334 = tf(phraseFreq=0.33333334)
      0.61370564 = idf(SearchField: cd=1 ef=1)
      1.0 = fieldNorm(field=SearchField, doc=0)

Without a boost  - 

0.07779912 = (MATCH) max of:
  0.07779912 = (MATCH) weight(spanNear([SearchField:cd, SearchField:ef], 10, false) in 0),
product of:
    0.3803083 = queryWeight(spanNear([SearchField:cd, SearchField:ef], 10, false)), product
of:
      0.61370564 = idf(SearchField: cd=1 ef=1)
      0.6196917 = queryNorm
    0.20456855 = (MATCH) fieldWeight(SearchField:spanNear([cd, ef], 10, false) in 0), product
of:
      0.33333334 = tf(phraseFreq=0.33333334)
      0.61370564 = idf(SearchField: cd=1 ef=1)
      1.0 = fieldNorm(field=SearchField, doc=0)


Regards,
Radha
-----Original Message-----
From: Steven A Rowe [mailto:sarowe@syr.edu] 
Sent: Thursday, April 16, 2009 10:35 PM
To: java-user@lucene.apache.org
Subject: RE: Need help : SpanNearQuery

Hi Radha,

On 4/16/2009 at 8:35 AM, Radhalakshmi Sredharan wrote:
> I have a question related to SpanNearQuery.
> 
> I need a hit even if there are 2/3 terms found with the span being
> applied for those 2 terms.
> 
> Is there any custom implementation in place for this? I checked
> SrndQuery but that also doesn't work.
> 
> This is my workaround currently:
> 
> 1)      For a list of terms ( ab,bc, cd,ef) , make a set like ( ab,bc)
> , ( bc,cd) ( ab,cd) (bc,ef) ( ab,bc,cd) ( ab,bc,cd,ef)..... and so on.
> 
> 2)      Create a spanNearQuery for  each of these terms
> 
> 3)      Add it to the booleanQuery with a  SHOULD clause.
> 
> However this approach gives me puzzling scores
>  eg If my document has  only ( ab,bc,cd) the penalty for the missing ef
> is very high and my score comes down quite a bit.

Do you know about the scoring documentation on the Lucene site: <http://lucene.apache.org/java/2_4_1/scoring.html>
?  In particular, see the link from there to the Searcher.explain() javadocs - this functionality
will help you understand what's happening with your queries.

I suspect that the penalty is due to fewer sub-queries matching; that is, not only does (ab,bc,cd,ef)
fail to match, but (ab,bc,ef), (ab,cd,ef), (ab,ef) etc. also fail to match, and since all
of these contribute to the final score, you will see a large drop off if you don't get a full
match.

Instead of putting all of the alternatives together in a single large disjunction, if you
package them such that the shorter alternatives don't influence the final score when larger
ones match, you may get something more like what you want.  I think DisjunctionMaxQuery <http://lucene.apache.org/java/2_4_1/api/org/apache/lucene/search/DisjunctionMaxQuery.html>,
along with judicious boosting, will do the trick, e.g.:

DMQ((ab,bc,cd,ef)^100,
    ((ab,bc,cd)^10 (ab,bc,ef)^10 (ab,cd,ef)^10 ...),
    ((ab,bc) (ab,cd) (ab,ef) ...))

Steve


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