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From "Robert Haschart (JIRA)" <j...@apache.org>
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 17:11:44 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1343?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12622607#action_12622607
] 

Robert Haschart commented on LUCENE-1343:
-----------------------------------------

The UnicodeNormalizationFilter does use the decompose normalization 
portion of the icu4j library as a starting point.  However even with 
that there are several instances where the normalizer code does not 
decompose a character into an unaccented character and a accent mark, a 
notable one being   ( Ł -> L )  so the UnicodeNormalizationFilter start 
with the approach you outlined, perform a decompose normalization 
followed by discarding all non-spacing modifier characters, and then can 
go on from there to further normalize the data by folding the additional 
characters that aren't handled by the decompose normalization onto their 
Latin1 lookalikes.

-Robert






> A replacement for ISOLatin1AccentFilter that does a more thorough job of removing 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
>            Reporter: Robert Haschart
>            Priority: Minor
>         Attachments: normalizer.jar, UnicodeCharUtil.java, UnicodeNormalizationFilter.java,
UnicodeNormalizationFilterFactory.java
>
>
> 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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