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From "Mark Miller (JIRA)" <>
Subject [jira] Commented: (LUCENE-1029) Illegal character replacements in ISOLatin1AccentFilter
Date Tue, 16 Oct 2007 03:53:50 GMT


Mark Miller commented on LUCENE-1029:

My comment about stemming was not meant to compare a stemmer to a diacritical stripper, but
rather to point out that the result of such an operation does not necessarily have to create
something 'legal' (just as a stemmer does not create 'legal' words). This was in response
to the comment 'Some of the ISOLatin1AccentFilter are legal while others are illegal. '

Your point about semantic meaning is well taken, but was not intended to be part of the comparison
I was going for. My bad. 

I think that the fact that ripping diacriticals can change the meaning of words goes without
saying...otherwise, why even have them in the language? As Uwe said, the main motivating factor
is to allow easy entry with the keyboard of another language. Of course this must come with
a compromise. Other search engines I have seen offer the exact functionality of this class.
(CPL, SearchServer, etc)

Literally, this thing is called an accent filter...letters go in, accents come off. Doing
more really does seem like a job for another class. If I can borrow a word I didn't know from
DM Smith, transliteration seems to go beyond an ISOLatin1AccentFilter. This is a tough sell
I know -- programmers seem to push the definition of filter to its limits and IMHO into the
realm of transform/translate.

Anyhow...I apologize for beating a dead horse...<g>

> Illegal character replacements in ISOLatin1AccentFilter
> -------------------------------------------------------
>                 Key: LUCENE-1029
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Analysis
>    Affects Versions: 2.2
>            Reporter: Marko Asplund
> The ISOLatin1AccentFilter class is responsible for replacing "accented characters in
the ISO Latin 1 character set by their unaccented equivalent".
> Some of the replacements performed for scandinavian characters (used e.g. in the finnish,
swedish, danish languages etc.) are illegal. The scandinavian characters are different from
the accented characters used e.g. in latin based languages such as french in that these characters
(ä, ö, å) represent entirely independent sounds in the language and therefore cannot be
represented with any other sound without change of meaning. It is therefore illegal to replace
these characters with any other character.
> This means for example that you can't change the finnish word sää (weather) to saa
(will have) because these are two entirely different words with different meaning. The same
applies to scandinavian languages as well.
> There's no connection between the sounds represented by ä and a; ö and o or å and
> In addition to the three characters mentioned above danish and norwegian use other special
characters such as ø and æ. It should be checked if the replacement is legal for these characters.

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