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From "Uwe Schindler" <...@thetaphi.de>
Subject RE: [jira] Commented: (LUCENE-2458) queryparser shouldn't generate phrasequeries based on term count
Date Sun, 23 May 2010 16:38:07 GMT
Same here, as already noted in the issue.

 

Uwe

 

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Uwe Schindler

H.-H.-Meier-Allee 63, D-28213 Bremen

 <http://www.thetaphi.de/> http://www.thetaphi.de

eMail: uwe@thetaphi.de

 

From: Shai Erera [mailto:serera@gmail.com] 
Sent: Sunday, May 23, 2010 6:34 PM
To: dev@lucene.apache.org
Subject: Re: [jira] Commented: (LUCENE-2458) queryparser shouldn't generate
phrasequeries based on term count

 

Robert - is the effect on scoring also on English and other European
languages? Or is it mostly for ngram-based languages, and especially CJK?

I want to stress that not all ngram-based languages are affected by this
behavior, especially those for which we do ngram just because of a lack of
good tokenizer.

That's why I'm not sure the default should be changed and I'm all for a
getter/setter. If however it turns out the default MUST be changed, then I
support the Version + getter/setter approach.

Shai

On Sun, May 23, 2010 at 6:00 PM, Uwe Schindler (JIRA) <jira@apache.org>
wrote:


   [
https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.pl
ugin.system.issuetabpanels:comment-tabpanel
<https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.p
lugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12870410#actio
n_12870410> &focusedCommentId=12870410#action_12870410 ]

Uwe Schindler commented on LUCENE-2458:
---------------------------------------

Hi Robert,

I also agree with Mark (as you know). We can have both:
- Version for a good default (3.1 will get the new non-phrase-query
behavior)
- A separate getsetter for this option
(set/getCreatePhraseQueryOnConcenattedTerms or whatever)

This would give you the best from both worlds.

> queryparser shouldn't generate phrasequeries based on term count
> ----------------------------------------------------------------
>
>                 Key: LUCENE-2458
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2458
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: QueryParser
>            Reporter: Robert Muir
>            Assignee: Robert Muir
>            Priority: Blocker
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2458.patch, LUCENE-2458.patch
>
>
> The current method in the queryparser to generate phrasequeries is wrong:
> The Query Syntax documentation
(http://lucene.apache.org/java/3_0_1/queryparsersyntax.html) states:
> {noformat}
> A Phrase is a group of words surrounded by double quotes such as "hello
dolly".
> {noformat}
> But as we know, this isn't actually true.
> Instead the terms are first divided on whitespace, then the analyzer term
count is used as some sort of "heuristic" to determine if its a phrase query
or not.
> This assumption is a disaster for languages that don't use whitespace
separation: CJK, compounding European languages like German, Finnish, etc.
It also
> makes it difficult for people to use n-gram analysis techniques. In these
cases you get bad relevance (MAP improves nearly *10x* if you use a
PositionFilter at query-time to "turn this off" for chinese).
> For even english, this undocumented behavior is bad. Perhaps in some cases
its being abused as some heuristic to "second guess" the tokenizer and piece
back things it shouldn't have split, but for large collections, doing things
like generating phrasequeries because StandardTokenizer split a compound on
a dash can cause serious performance problems. Instead people should analyze
their text with the appropriate methods, and QueryParser should only
generate phrase queries when the syntax asks for one.
> The PositionFilter in contrib can be seen as a workaround, but its pretty
obscure and people are not familiar with it. The result is we have bad
out-of-box behavior for many languages, and bad performance for others on
some inputs.
> I propose instead that we change the grammar to actually look for double
quotes to determine when to generate a phrase query, consistent with the
documentation.

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