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From "Chuck Williams (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-323) [PATCH] MultiFieldQueryParser and BooleanQuery do not provide adequate support for queries across multiple fields
Date Wed, 21 Dec 2005 04:58:32 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-323?page=comments#action_12361018 ] 

Chuck Williams commented on LUCENE-323:
---------------------------------------

FYI, I've recently noticed the new implementation of MultiFieldQueryParser (new to me since
I was out of touch for about 6 months or so).  This now does the distribution, so I'm no longer
of the opinion that DistributingMultiFieldQueryParser should be committed.  A better approach
would be to generalize MultiFieldQueryParser to be able use MaxDisjunctionQuery as its container
instead of BooleanQuery in the appropriate places.  FYI, I'll look at this soon and will submit
a revised patch unless there is some reason the details don't sort out.  Even it that case,
the same approach used in MultiFieldQueryParser of specializing certain methods of QueryParser
could be used for DistributingMultiFieldQueryParser, rather than the post parsing traversal/transformation
it currently does.


> [PATCH] MultiFieldQueryParser and BooleanQuery do not provide adequate support for queries
across multiple fields
> -----------------------------------------------------------------------------------------------------------------
>
>          Key: LUCENE-323
>          URL: http://issues.apache.org/jira/browse/LUCENE-323
>      Project: Lucene - Java
>         Type: Bug
>   Components: QueryParser
>     Versions: 1.4
>  Environment: Operating System: Windows XP
> Platform: PC
>     Reporter: Chuck Williams
>     Assignee: Lucene Developers
>  Attachments: DisjunctionMaxQuery.java, DisjunctionMaxScorer.java, TestDisjunctionMaxQuery.java,
TestMaxDisjunctionQuery.java, TestRanking.zip, TestRanking.zip, TestRanking.zip, WikipediaSimilarity.java,
WikipediaSimilarity.java, WikipediaSimilarity.java, dms.tar.gz
>
> The attached test case demonstrates this problem and provides a fix:
>   1.  Use a custom similarity to eliminate all tf and idf effects, just to 
> isolate what is being tested.
>   2.  Create two documents doc1 and doc2, each with two fields title and 
> description.  doc1 has "elephant" in title and "elephant" in description.  
> doc2 has "elephant" in title and "albino" in description.
>   3.  Express query for "albino elephant" against both fields.
> Problems:
>       a.  MultiFieldQueryParser won't recognize either document as containing 
> both terms, due to the way it expands the query across fields.
>       b.  Expressing query as "title:albino description:albino title:elephant 
> description:elephant" will score both documents equivalently, since each 
> matches two query terms.
>   4.  Comparison to MaxDisjunctionQuery and my method for expanding queries 
> across fields.  Using notation that () represents a BooleanQuery and ( | ) 
> represents a MaxDisjunctionQuery, "albino elephant" expands to:
>         ( (title:albino | description:albino)
>           (title:elephant | description:elephant) )
> This will recognize that doc2 has both terms matched while doc1 only has 1 
> term matched, score doc2 over doc1.
> Refinement note:  the actual expansion for "albino query" that I use is:
>         ( (title:albino | description:albino)~0.1
>           (title:elephant | description:elephant)~0.1 )
> This causes the score of each MaxDisjunctionQuery to be the score of highest 
> scoring MDQ subclause plus 0.1 times the sum of the scores of the other MDQ 
> subclauses.  Thus, doc1 gets some credit for also having "elephant" in the 
> description but only 1/10 as much as doc2 gets for covering another query term 
> in its description.  If doc3 has "elephant" in title and both "albino" 
> and "elephant" in the description, then with the actual refined expansion, it 
> gets the highest score of all (whereas with pure max, without the 0.1, it 
> would get the same score as doc2).
> In real apps, tf's and idf's also come into play of course, but can affect 
> these either way (i.e., mitigate this fundamental problem or exacerbate it).

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