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From "Simon Willnauer (JIRA)" <>
Subject [jira] Commented: (LUCENE-2458) queryparser shouldn't generate phrasequeries based on term count
Date Sun, 23 May 2010 09:08:17 GMT


Simon Willnauer commented on LUCENE-2458:

bq. FWIW, I agree w/ Mark. I don't think it's a bug, but more of a user option
I would rather agree with Shai and Mark here but it is also not the behavior I would expect
if I come to lucene the first time and use query parser. I still don't understand why this
should not be done by using version. Exactly stuff like that where the reason to introduce
it. Using Version to change runtime behavior has been done before (see CharTokenizer, CharacterUtils,
LowerCaseFilter). IMO this is a totally valid usage and makes people aware of that something
has changed. I also figured that Version seriously got adopted in the Community, people start
using and appreciating it which somewhat changed my mind on Version.

bq. And for what's it's also worth, we've once worked w/ a Japanese linguist,
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. It should give the majority of users a good
DEFAULT and has never aimed to be a perfect solution. I usually recommend to misplease everybody
equally than being biased towards a certain usergroup when providing an API which is not super
special purpose.

It seems to me making this behavior available with Version is the right way to go. I don't
care if people call it a bug or a good default for US text - what count is to give people
a good default no matter what they index or where they come from. (sounds like this is close
to discriminating people - just kidding)

Another thing i wanna mention is that QueryParser should really be in contrib / modules rather
than in core. I don't know how many parsers we have in the meanwhile but we should really
consolidate them in a new module for 4.0. Get the stuff out there, make a copy of the current
parser, name it "SmartENBiasedAutomaticPhraseGeneratingQueryParser", fix that in the other
one and provide people a good default.

just my $0.05

> queryparser shouldn't generate phrasequeries based on term count
> ----------------------------------------------------------------
>                 Key: LUCENE-2458
>                 URL:
>             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 (
> {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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