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