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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2458) queryparser shouldn't generate phrasequeries based on term count
Date Sun, 23 May 2010 10:39:16 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12870384#action_12870384
] 

Shai Erera commented on LUCENE-2458:
------------------------------------

bq. There will be tons of different opinions to that around linguists around the world but
this parser is not for linguists in the first place.

Sure. I've pointed that out just to show there are different opinions around that particular
problem.

bq. It seems to me making this behavior available with Version is the right way to go

I disagree (and agree w/ Mark). Version can only control default behavior. This particular
issue should be a setter IMO. Irregardless of what the default behavior is, I may want to
set it differently. It doesn't make sense to *guess* what Version should I use in order to
get that behavior.

That's why I don't mind leaving the current behavior as default, and introduce a setter for
whoever wants to change it. The current behavior is not applicable for just English - I bet
there's a whole list of languages which would interpret that query the same (i.e. require
a phrase to be generated).

And I don't know the distribution of Lucene users around the world, but I'm not sure that
CJK users are more common that say English ones, or other European languages. So who knows
what a good default is? :)

I suggest we leave the default as it is now, and introduce a setter. People have been working
w/ the parser and that default for a long time. Why suddenly change it?

> 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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