Time Zone Localizations

Paul Eggert eggert at CS.UCLA.EDU
Mon Jun 14 04:37:01 UTC 2004

"Mark Davis" <mark.davis at jtcsv.com> writes:

> For any given locale, we would disallow a collision between
> names. Thus for the locale en (English) we can't have AST mean both
> Alaska Standard Time and Atlantic Standard Time.

That collides with common practice in Australia, which is to use "EST"
to denote both "Eastern Standard Time" and "Eastern Summer Time".  The
tz database attempts to support common practice as much as possible,
so if your system doesn't allow this sort of thing you'll have to make
some special provision for the discrepancies.

>>   For example "Pacific War Time" should be used for daylight-saving
>>   time in Los Angeles from 1942-02-09 through 1945-08-14.
> At this point, we are not really interested in translations of the way that
> certain TZIDs would have been named in the past;

I sense a problem in terminology here.  The TZID is the same either
way: it's "America/Los_Angeles".  The problem is merely that Los
Angeles has different names for daylight-saving time, depending on the
time stamp in question.  Even if I'm writing today, it's incorrect for
me to write the phrase "January 20, 1943, at 8:00am Pacific Daylight
Time" in Los Angeles: I should write "Pacific War Time" instead.

Another example: in 1988 Newfoundland observed double-daylight time
(two hours ahead of normal), which the tz database calls "NDDT"
instead of the usual "NDT".  It could happen again.  You may not want
to support double-daylight saving time, but if so you should note down
the problem somewhere.

> I had thought that to get all the timezones that are in use in the
> world, including those in international waters, wouldn't we have to
> include the Etc/GMT* ones? Or is this wrong?

In international waters, my understanding is that local time is
entirely at the whim of the ship's captain.  (So you may have to
support all the POSIX TZIDs after all.  :-) I suppose the Olson
Etc/GMT* TZIDs are better than nothing, but they weren't intended to
be (and are not) a complete list of time zone offsets in actual use,
whether in international waters or anywhere else.

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