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From "Robert Muir (JIRA)" <>
Subject [jira] Updated: (LUCENE-1488) issues with standardanalyzer on multilingual text
Date Fri, 12 Dec 2008 05:58:44 GMT


Robert Muir updated LUCENE-1488:

    Attachment: ICUAnalyzer.patch

i've attached a patch for 'ICUAnalyzer'. I see that some things involving Token have changed
but I created it before that point.

I stole the unit tests from standard analyzer and put comments as to why certain ones arent
appropriate and disabled those.

i added some unit tests that demonstrate some of the value, correct analysis for arabic numerals,
hindi text, decomposed latin diacritics, hebrew punctuation, cantonese and linear-b text outside
of the BMP, etc.

one issue is that setMaxTokenLength() doesnt work correctly for values > 255 because CharTokenizer
has a hardcoded private limit of 255 that i can't override. This is a problem since i use
WhitespaceTokenizer first and then break down those tokens with the RBBI.

> issues with standardanalyzer on multilingual text
> -------------------------------------------------
>                 Key: LUCENE-1488
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Wish
>          Components: contrib/analyzers
>            Reporter: Robert Muir
>            Priority: Minor
>         Attachments: ICUAnalyzer.patch
> The standard analyzer in lucene is not exactly unicode-friendly with regards to breaking
text into words, especially with respect to non-alphabetic scripts.  This is because it is
unaware of unicode bounds properties.
> I actually couldn't figure out how the Thai analyzer could possibly be working until
i looked at the jflex rules and saw that codepoint range for most of the Thai block was added
to the alphanum specification. defining the exact codepoint ranges like this for every language
could help with the problem but you'd basically be reimplementing the bounds properties already
stated in the unicode standard. 
> in general it looks like this kind of behavior is bad in lucene for even latin, for instance,
the analyzer will break words around accent marks in decomposed form. While most latin letter
+ accent combinations have composed forms in unicode, some do not. (this is also an issue
for asciifoldingfilter i suppose). 
> I've got a partially tested standardanalyzer that uses icu Rule-based BreakIterator instead
of jflex. Using this method you can define word boundaries according to the unicode bounds
properties. After getting it into some good shape i'd be happy to contribute it for contrib
but I wonder if theres a better solution so that out of box lucene will be more friendly to
non-ASCII text. Unfortunately it seems jflex does not support use of these properties such
as [\p{Word_Break = Extend}] so this is probably the major barrier.
> Thanks,
> Robert

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