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https://issues.apache.org/jira/browse/LUCENE-1343?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786712#action_12786712
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Ken Krugler commented on LUCENE-1343:
-------------------------------------
Just to make sure this point doesn't get lost in the discussion over
normalization - the issue of "visual normalization" is one that I think
ISOLatin1AccentFilter originally was trying to address. Specifically how to
fold together forms of letters that a user, when typing, might consider
equivalent.
This is indeed language specific, and re-implementing support that's already in
ICU4J is clearly a Bad Idea.
I think there's value in a general normalizer that implements the Unicode
Consortium's algorithm/data for normalization of int'l domain names, as this is
intended to avoid visual spoofing of domain names.
Don't know/haven't tracked if or when this is going into ICU4J. But (similar to
ICU generic sorting) it provides a useful locale-agnostic approach that would
work well-enough for most Lucene use cases.
> 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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