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From "Steven Rowe (JIRA)" <>
Subject [jira] Commented: (LUCENE-1126) Simplify StandardTokenizer JFlex grammar
Date Thu, 04 Sep 2008 16:13:44 GMT


Steven Rowe commented on LUCENE-1126:

Could we, alternatively, modify the patch to explicitly add back in the full Thai range into
ALPHANUM, and then upgrade to \p{Alphabetic} once the next version of JFlex is released?

Or are there other languages, besides Thai, that we might break with this patch?

I noticed in looking at the Unicode database that Lao, which is contiguous with Thai and contained
in the unpatched {{{LETTER}}} range, has exactly the same issue as Thai.  However, the Lucene
code base doesn't contain a Lao Analyzer.  And I think ThaiAnalyzer is depending on faulty
behavior from StandardTokenizer, so "fixing" the issue for other languages would be to make
the assumption that they too would depend on bad behavior.

I'll shortly provide a redone patch that allows the ThaiAnalyzer to work again, but unless
we have evidence of actual use by other language analyzers, I don't think we should be addressing
them right now.

> Simplify StandardTokenizer JFlex grammar
> ----------------------------------------
>                 Key: LUCENE-1126
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>    Affects Versions: 2.2
>            Reporter: Steven Rowe
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.4
>         Attachments: LUCENE-1126.patch
> Summary of thread entitled "Fullwidth alphanumeric characters, plus a question on Korean
ranges" begun by Daniel Noll on java-user, and carried over to java-dev:
> On 01/07/2008 at 5:06 PM, Daniel Noll wrote:
> > I wish the tokeniser could just use Character.isLetter and
> > Character.isDigit instead of having to know all the ranges itself, since
> > the JRE already has all this information.  Character.isLetter does
> > return true for CJK characters though, so the ranges would still come in
> > handy for determining what kind of letter they are.  I don't support
> > JFlex has a way to do this...
> The DIGIT macro could be replaced by JFlex's predefined character class [:digit:], which
has the same semantics as java.lang.Character.isDigit().
> Although JFlex's predefined character class [:letter:] (same semantics as java.lang.Character.isLetter())
includes CJK characters, there is a way to handle this using JFlex's regex negation syntax
{{!}}.  From [the JFlex documentation|]:
> bq. [T]he expression that matches everything of {{a}} not matched by {{b}} is !(!{{a}}|{{b}})

> So to exclude CJ characters from the LETTER macro:
> {code}
>     LETTER = ! ( ! [:letter:] | {CJ} )
> {code}
> Since [:letter:] includes all of the Korean ranges, there's no reason (AFAICT) to treat
them separately; unlike Chinese and Japanese characters, which are individually tokenized,
the Korean characters should participate in the same token boundary rules as all of the other
> I looked at some of the differences between Unicode 3.0.0, which Java 1.4.2 supports,
and Unicode 5.0, the latest version, and there are lots of new and modified letter and digit
ranges.  This stuff gets tweaked all the time, and I don't think Lucene should be in the business
of trying to track it, or take a position on which Unicode version users' data should conform
> Switching to using JFlex's [:letter:] and [:digit:] predefined character classes ties
(most of) these decisions to the user's choice of JVM version, and this seems much more reasonable
to me than the current status quo.
> I will attach a patch shortly.

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