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From "Robert Muir (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 Mon, 07 Dec 2009 15:31:18 GMT


Robert Muir commented on LUCENE-1343:

bq. Robert Muir, Would it make sense to have a Greek filter that strips diacritics? My thought
is that if the letter is Greek then the diacritics would be removed, but otherwise it would

The GreekLowerCaseFilter (incorrectly named) does this also, somewhat. it removes tone marks...
but this might not be what you "want" (depending on what that is), if you are dealing with
polytonic Greek (sorry for my ignorance of the biblical test you are looking at, but I think
it is ancient Greek?)

bq. Similar question for Hebrew, I see value in two filters: one would strip cantillation
and the other, vowel points. Or would it be better to have one that can do both depending
on flags?

This depends on your use case, and then you have dagesh,shin dot, too... These are all NSMs.
But this is going to depend on the user, and I think every person will need their own, they
can use CharFilter or other ways of defining these tables.

> 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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