AW: AW: AW: sharp s (Eszett)

Martin Duerst duerst at
Thu Mar 13 09:33:31 CET 2008

At 10:13 08/03/12, Kenneth Whistler wrote:
>------------- Begin Forwarded Message -------------

>Georg Ochsner asked:

>> Can you explain for which applications in particular the 
>> case-insensitivity for domain names is essential, and why?
>Well others may have a more informed opinion, but it seems
>to me that it would be just about all of them, since
>traditionally (not even speaking of IDN's) domain names
>have always been case-insensitive. So:
>and even
>all ought to resolve to the same domain.

Of course, all of the above indeed do, and that's why we
expect them to do. But I think the question was about
applications. E.g. is there any particular application or use
case where it is crucial to have domain names in all upper

I think saying that domain names always have been case-insensitive
is in some way putting the chart before the horse.

What was done with domain names was that it was observed
that certain groups (pairs, in fact) of letters were used
virtually interchangeably. It was decided that the system
would match these for user convenience, while keeping the
distinction of which variant was registered. It turned out
that these pairs of letters were related by case, and that
the shortest way to characterize this behavior was to say
that domain names are case-independent.

Extending the repertoire for domain names means that decisions
should not just be based on using the same general concept/
label/data file as for the basic Latin case. That may be
a good starting point, but as I have explained in my mail
about exceptions, human script usage is very varied.
Rather than saying "domain names are case insensitive,
what's the closest we can do for case insensitive for
the sharp s", we should say "what's the best way
(within the very general constraints of the DNS) to
make sure that those characters that users think of
as pretty fundamentally different are treated as different,
whereas those characters that users see as virtually the
same are treated as one".

If the result of that consideration is case-insensitivity
(as defined by a particular table) for that case, that's
of course fine, but there may be other results. Immagine
a script with a case distinction, but where there is a
very firm tradition to use upper-case for official,
government-related names, and lower-case for company and
private names. In such a (hypothetical) case, it would
probably better to treat that script as case-sensitive
in DNS.

>> Can such applications make use of the new uppercase sharp S 
>> in Unicode 5.1?
>No, because its case mapping will necessarily be even more
>defective than that for the existing lowercase sharp S.
>All the addition of uppercase sharp S does is add one
>more element to the case folding equivalence class:
>{゜, capital-゜, ss, SS}. It does not (and cannot) create
>new, clean case pairs.

[Cutting out backwards compatibility issues, which can
be solved (as Cary has explained well).]

>And I think that is why Mark wants to make sure that we
>have DE-NIC and all the other German stakeholders explicitly
>on board for any change that would potentially have these
>kinds of impacts for German domain names.

"all" stakeholders is probably going a bit too far, but it's
very clear that input from a lot of viewpoints is highly

Regards,   Martin.

#-#-#  Martin J. Du"rst, Assoc. Professor, Aoyama Gakuin University
#-#-#       mailto:duerst at     

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