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https://issues.apache.org/jira/browse/LUCENE-1302?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12603925#action_12603925
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Hoss Man commented on LUCENE-1302:
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bq. The one thing that bothers me still is that the BTQ sub-expl would print as
MATCH when in fact it just hurts the current doc score (apparently "not
enough"). Would it be more correct for the (negative) BTQ part to say
"NON-MATCH"?
Bottom Line: if "next()" stops on a doc, then the Explanation for that doc
should indicate a "MATCH" ... regardless of what the score is.
the the Explanation by BTQ indicates it's a "NON-MACH" even thought the BTQ
Scorer would return it as a "hit" when searching, that would screw up the
Explanation generated by a BooleanQuery. Consider a 3 clause BooleanQuery with
minNrShouldMath set to 2. one of the clauses only matches doc#42, one of the
clauses matches no docs, and the third clause is a BTQ -- if the Explanation
for the BTQ says NO_MATCH for doc#42 just because it has a negative score then
the BooleanQuery Explanation is going to say the wrong thing.
> explain should not mask negative scores
> ---------------------------------------
>
> Key: LUCENE-1302
> URL: https://issues.apache.org/jira/browse/LUCENE-1302
> Project: Lucene - Java
> Issue Type: Bug
> Components: Query/Scoring
> Reporter: Doron Cohen
> Assignee: Doron Cohen
> Priority: Minor
> Fix For: 2.4
>
> Attachments: lucene-1302-explain-negative.patch
>
>
> Explanation.isMatch() returns false for 0 or negative scores.
> Hence negative scores are omitted from the explanation.
> This causes, when using e.g. BoostingTermQuery with negative boosts, a
> difference between the collected doc score and the score shown by explain().
> A word on the usage of this - BTQ with negative boosts is useful for
> "punishing" documents for containing a term. It also allows all sorts of
> tricks with multiplying query boost by the BTQ boost, so you get a positive
> score if both boosts have the same sign but negative otherwise. - I am sure
> there other uses as well.
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