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Date: Fri, 22 Feb 2008 02:34:19 -0800 (PST)
From: =?utf-8?Q?Christian_Kohlsch=C3=BCtter_=28JIRA=29?= <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-954) Toggle score normalization in Hits
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    [ https://issues.apache.org/jira/browse/LUCENE-954?page=3Dcom.atlassian=
.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D1257=
1339#action_12571339 ]=20

Christian Kohlsch=C3=BCtter commented on LUCENE-954:
-----------------------------------------------

You are right, Yonik.

Hits currently tries to "hide" this by normalizing the scores to a maximum =
of 1, simply by dividing the "raw" scores by the maximum score returned.

This is why the scores from Hits are currently not comparable to each other=
. The suggested patch resolves this problem.


> Toggle score normalization in Hits
> ----------------------------------
>
>                 Key: LUCENE-954
>                 URL: https://issues.apache.org/jira/browse/LUCENE-954
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>    Affects Versions: 2.2
>         Environment: any
>            Reporter: Christian Kohlsch=C3=BCtter
>         Attachments: hits-scoreNorm.patch
>
>
> The current implementation of the "Hits" class sometimes performs score n=
ormalization.
> In particular, whenever the top-ranked score is bigger than 1.0, it is no=
rmalized to a maximum of 1.0.
> In this case, Hits may return different score results than TopDocs-based =
methods.
> In my scenario (a federated search system), Hits delievered just plain wr=
ong results.
> I was merging results from several sources, all having homogeneous statis=
tics (similar to MultiSearcher, but over the Internet using HTTP/XML-based =
protocols).
> Sometimes, some of the sources had a top-score greater than 1, so I ended=
 up with garbled results.
> I suggest to add a switch to enable/disable this score-normalization at r=
untime.
> My patch (attached) has an additional peformance benefit, since score nor=
malization now occurs only when Hits#score() is called, not when creating t=
he Hits result list. Whenever scores are not required, you save one multipl=
ication per retrieved hit (i.e., at least 100 multiplications with the curr=
ent implementation of Hits).

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