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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2458) queryparser shouldn't generate phrasequeries based on term count
Date Wed, 12 May 2010 17:40:42 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866648#action_12866648
] 

Robert Muir commented on LUCENE-2458:
-------------------------------------

{quote}
As described in another recent
thread, this allows a search for 'example.com' to match a document which
contains the URL 'http://www.example.com/index.html'. It would suck if all of
a sudden a search for 'example.com' started matching every document that
contained 'com'.
{quote}

You could solve this with better analysis, for example recognizing the full URL and decomposing
it into its parts (forming n-grams of them).
This would be more performant than the current "english hacking" anyway.

I'm honestly having a tough time seeing where to proceed on this issue.

Lucene's queryparsing is completely broken for several languages due to this bug, and such
language-specific hacking (heuristically forming phrase queries based on things that people
subjectively feel helps for english) really doesn't belong in core lucene, but instead elsewhere,
perhaps in some special optional pass to the control query parser.

The queryparser really should be language-independent and work well on average, this would
fix it for several languages.

However, given the *huge* english bias I see here, i have a tough time seeing what concrete
direction (e.g. code) i can work on to try to fix it. I feel such work would only be rejected
since so many people seem opposed to simplifying the query parser and removing this language-specific
hack.

If someone brings up an issue with the query parser (for instance i brought up several language-specific
problems at apachecon), then people are quick to say that this doesn't belong in the queryparser,
but should be dealt with on a special case. Why isn't english treated this way too? I don't
consider this bias towards english "at all costs" including preventing languages such as Chinese
from working at all very fair, I think its a really ugly stance for Lucene to take.



> 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
>            Priority: Critical
>
> 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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