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From: Paul Elschot <paul.elschot@xs4all.nl>
To: java-user@lucene.apache.org
Subject: Re: PhraseQuery issues - differences with SpanNearQuery
Date: Fri, 5 Sep 2008 01:21:35 +0200
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Op Thursday 04 September 2008 20:39:13 schreef Mark Miller:
> Sounds like its more in line with what you are looking for. If I
> remember correctly, the phrase query factors in the edit distance in
> scoring, but the NearSpanQuery will just use the combined idf for
> each of the terms in it, so distance shouldnt matter with spans (I'm
> sure Paul will correct me if I am wrong).

SpanScorer will use the similarity slop factor for each matching
span size to adjust the effective frequency.
The span size is the difference in position between the first
and last matching term, and idf is not used for scoring Spans.
The reason why idf is not used could be that there is no basic
score value associated with inner spans; only top level spans
are scored by SpanScorer.
For more details, please consult the SpanScorer code.

Regards,
Paul Elschot

>
> - Mark
>
> Yannis Pavlidis wrote:
> > Hi,
> >
> > I am having an issue when using the PhraseQuery which is best
> > illustrated with this example:
> >
> > I have created 2 documents to emulate URLs. One with a URL of:
> > "http://www.airballoon.com" and title "air balloon" and the second
> > one with URL "http://www.balloonair.com" and title: "balloon air".
> >
> > Test1 (PhraseQuery)
> > ======
> > Now when I use the phrase query with - title: "air balloon" ~2
> > I get back:
> >
> > url: "http://www.airballoon.com" - score: 1.0
> > url: "http://www.balloonair.com" - score: 0.57
> >
> > Test2 (PhraseQuery)
> > ======
> > Now when I use the phrase query with - title: "balloon air" ~2
> > I get back:
> > url: "http://www.balloonair.com" - score: 1.0
> > url: "http://www.airballoon.com" - score: 0.57
> >
> > Test3 (PhraseQuery)
> > ======
> > Now when I use the phrase query with - title: "air balloon" ~2
> > title: "balloon air" ~2 I get back:
> > url: "http://www.airballoon.com" - score: 1.0
> > url: "http://www.balloonair.com" - score: 1.0
> >
> > Test4 (SpanNearQuery)
> > =======
> > spanNear([title:air, title:balloon], 2, false)
> > I get back:
> > url: "http://www.airballoon.com" - score: 1.0
> > url: "http://www.balloonair.com" - score: 1.0
> >
> > I would have expected that Test1, Test2 would actually return both
> > URLs with score of 1.0 since I am setting the slop to 2. It seems
> > though that lucene really favors and absolute exact match.
> >
> > Is it safe to assume that for what I am looking for (basically
> > score the docs the same regardless on when someone is searching for
> > "air balloon" or "balloon air") it would be better to use the
> > SpanNearQuery rather than the PhraseQuery?
> >
> > Any input would be appreciated.
> >
> > Thanks in advance,
> >
> > Yannis.
>
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