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From "Ken Krugler (JIRA)" <>
Subject [jira] Commented: (LUCENE-1343) A replacement for ISOLatin1AccentFilter that does a more thorough job of removing diacritical marks or non-spacing modifiers.
Date Thu, 14 Aug 2008 03:49:44 GMT


Ken Krugler commented on LUCENE-1343:

Hi Robert,

FWIW, the issues being discussed here are very similar to those covered by the [Unicode Security
Considerations|] technical report #36, and associated
data found in the [Unicode Security Mechanisms|] technical
report #39.

The fundamental issue for int'l domain name spoofing is detecting when two sequences of Unicode
code points will render as similar glyphs...which is basically the same issue you're trying
to address here, so that when you search for something you'll find all terms that "look" similar.

So for a more complete (though undoubtedly slower & bigger) solution, I'd suggest using
ICU4J to do a NFKD normalization, then toss any combining/spacing marks, lower-case the result,
and finally apply mappings using the data tables found in the technical report #39 referenced

-- Ken

> A replacement for ISOLatin1AccentFilter that does a more thorough job of removing diacritical
marks or non-spacing modifiers.
> -----------------------------------------------------------------------------------------------------------------------------
>                 Key: LUCENE-1343
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>            Reporter: Robert Haschart
>            Priority: Minor
>         Attachments: normalizer.jar,,,
> The ISOLatin1AccentFilter takes Unicode characters that have diacritical marks and replaces
them with a version of that character with the diacritical mark removed.  For example é becomes
e.  However another equally valid way of representing an accented character in Unicode is
to have the unaccented character followed by a non-spacing modifier character (like this:
 é  )    The ISOLatin1AccentFilter doesn't handle the accents in decomposed unicode characters
at all.    Additionally there are some instances where a word will contain what looks like
an accented character, that is actually considered to be a separate unaccented character 
such as  Ł  but which to make searching easier you want to fold onto the latin1  lookalike
 version   L  .   
> The UnicodeNormalizationFilter can filter out accents and diacritical marks whether they
occur as composed characters or decomposed characters, it can also handle cases where as described
above characters that look like they have diacritics (but don't) are to be folded onto the
letter that they look like ( Ł  -> L )

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