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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1696) Added New Token API impl for ASCIIFoldingFilter
Date Tue, 16 Jun 2009 15:41:07 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12720193#action_12720193
] 

Robert Muir commented on LUCENE-1696:
-------------------------------------

simon, actually i think its documented you can use ENGLISH collator and it will behave like
asciifolding filter (simply remove all diacritics).
you could then apply the tailorings like the example and get the behavior you want, versus
maintaining a custom asciifoldingfilter...

> Added New Token API impl for ASCIIFoldingFilter
> -----------------------------------------------
>
>                 Key: LUCENE-1696
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1696
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>    Affects Versions: 2.9
>            Reporter: Simon Willnauer
>            Assignee: Mark Miller
>             Fix For: 2.9
>
>         Attachments: ASCIIFoldingFilter._newTokenAPI.patch, TestGermanCollation.java
>
>
> I added an implementation of incrementToken to ASCIIFoldingFilter.java and extended the
existing  testcase for it.
> I will attach the patch shortly.
> Beside this improvement I would like to start up a small discussion about this filter.
ASCIIFoldingFitler is meant to be a replacement for ISOLatin1AccentFilter which is quite nice
as it covers a superset of the latter. I have used this filter quite often but never on a
as it is basis. In the most cases this filter does the correct thing (replace a special char
with its ascii correspondent) but in some cases like for German umlaut it does not return
the expected result. A german umlaut  like 'ä' does not translate to a but rather to 'ae'.
I would like to change this but I'n not 100% sure if that is expected by all users of that
filter. Another way of doing it would be to make it configurable with a flag. This would not
affect performance as we only check if such a umlaut char is found. 
> Further it would be really helpful if that filter could "inject" the original/unmodified
token with the same position increment into the token stream on demand. I think its a valid
use-case to index the modified and unmodified token. For instance, the german word "süd"
would be folded to "sud". In a query q:(süd) the filter would also fold to sud and therefore
find sud which has a totally different meaning. Folding works quite well but for special cases
would could add those options to make users life easier. The latter could be done in a subclass
while the umlaut problem should be fixed in the base class.
> simon 

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