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From "Uwe Schindler (JIRA)" <>
Subject [jira] Commented: (LUCENE-1029) Illegal character replacements in ISOLatin1AccentFilter
Date Mon, 15 Oct 2007 10:40:50 GMT


Uwe Schindler commented on LUCENE-1029:

This is true for other european languages, too. In Germany it is also a difference between
"ä" and "a" (it sounds different). A correct replacement in German would be to replace "ä"
by "ae" (two chars).
But I think it is not a problem. The real use of this filter is to enable people coming from
other countries without the keys on their keyboard to search in a lucene index. Many americans
for example search for the German last name "Müller" always by typing "Muller", because they
cannot enter the umlaut. In Scandianian languages it will be the same, they would enter "o"
instead of "ø". The accent filter is just to enable this. If you create an index just for
one scandinavian country, just leave this filter out.
And in principle it is no problem to find documents that does not match the entered keywords
The filter is the same like the Soundex filter. After a transformation to soundex the word
lokks different and has never his original meaning :)

> 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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