[tz] Converting from individual cities/states/country names to Windows time zone names

[yoshito_umaoka at us.ibm.com]

> What I have been able to find is a way to convert from TZID (Olsen) 
> to Windows 
> timezone IDs using this URL:
> http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/zone_tzid.html

I'm planning to update the data to support multiple TZID mapping (One 
Windows TZ -> Multiple TZIDs) in CLDR. I was considering this before, but 
it's quite a tough task (also keeping data up-to-date is not trivial).

It looks you're trying to create mapping data from location to Windows 
time zone. You would find how difficult to achieve this soon.

There are several type of issues.

1) No matching UTC offset in Windows

For example, Australia/Eucla uses UTC+08:45 as base offset, but there is 
no such zones in Windows time zone list. There are several other 
instances.


2) No matching daylight saving time rule in Windows

For example, Pacific/Easter observes daylight saving time from August, 
2011 to March 2012. However, Windows does not have any UTC-06:00 zones 
supporting the daylight saving time rules (Windows UTC-06:00 zones are all 
Northern Hemisphere type rules).


3) Ambiguous mapping

For example, Windows has following time zones with UTC+09:00 / no DST.

(UTC+09:00) Osaka, Sapporo, Tokyo
(UTC+09:00) Irkutsk
(UTC+09:00) Seoul

You have to decide one from above for some other territories using 
UTC+09:00/no DST. For example, Asia/Dili, Asia/Jayapura, Pacific/Palau.


4) Out of date data

You may want to map Belarus to (UTC+02:00) Minsk. However, Minsk (Belarus) 
is currently using UTC+03:00/no DST.
Microsoft suggests Windows users in Belarus to use (UTC+03:00) Kakiningrad 
for now [http://support.microsoft.com/kb/2625508].


-Yoshito
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