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Date: Tue, 20 Apr 2010 09:52:52 -0400 (EDT)
From: "Robert Muir (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-1343) A replacement for
 AsciiFoldingFilter that does a more thorough job of removing diacritical
 marks or non-spacing modifiers.
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    [ https://issues.apache.org/jira/browse/LUCENE-1343?page=3Dcom.atlassia=
n.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D128=
58891#action_12858891 ]=20

Robert Muir commented on LUCENE-1343:
-------------------------------------

By the way, I have been running this with the ASCIIFoldingFilter tests and =
ensuring its a superset (e.g. we have at least all their mappings).

But there are some bugs in ASCIIFoldingFilter that should be fixed:

For example, U+1E9B (LATIN SMALL LETTER LONG S WITH DOT ABOVE)
But in unicode. this is canonically equivalent to U+017F (LONG S) U+0307 (C=
OMBINING DOT ABOVE)
AsciiFoldingFilter folds U+1E9B (LONG S WITH DOT) to an F
but it folds U+017F (LONG S) to an S

Unicode defines this character as a compatibility equivalent to S anyway, b=
ut its worse that ASCIIFoldingFilter is canonically inconsistent with itsel=
f.


> A replacement for AsciiFoldingFilter that does a more thorough job of rem=
oving diacritical marks or non-spacing modifiers.
> -------------------------------------------------------------------------=
-------------------------------------------------
>
>                 Key: LUCENE-1343
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1343
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>    Affects Versions: 3.1
>            Reporter: Robert Haschart
>            Assignee: Robert Muir
>            Priority: Minor
>             Fix For: 3.1
>
>         Attachments: LUCENE-1343.patch, normalizer.jar, UnicodeCharUtil.j=
ava, UnicodeNormalizationFilter.java, UnicodeNormalizationFilterFactory.jav=
a, utr30.nrm
>
>
> The ISOLatin1AccentFilter takes Unicode characters that have diacritical =
marks and replaces them with a version of that character with the diacritic=
al mark removed.  For example =C3=A9 becomes e.  However another equally va=
lid way of representing an accented character in Unicode is to have the una=
ccented character followed by a non-spacing modifier character (like this: =
 =C3=A9  )    The ISOLatin1AccentFilter doesn't handle the accents in decom=
posed unicode characters at all.    Additionally there are some instances w=
here a word will contain what looks like an accented character, that is act=
ually considered to be a separate unaccented character  such as  =C5=81  bu=
t which to make searching easier you want to fold onto the latin1  lookalik=
e  version   L  .  =20
> The UnicodeNormalizationFilter can filter out accents and diacritical mar=
ks whether they occur as composed characters or decomposed characters, it c=
an also handle cases where as described above characters that look like the=
y have diacritics (but don't) are to be folded onto the letter that they lo=
ok like ( =C5=81  -> L )

--=20
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