Timezone translations

Robert Elz kre at munnari.OZ.AU
Mon Jun 6 02:57:29 UTC 2005

    Date:        Sun, 5 Jun 2005 17:36:33 -0700
    From:        "Mark Davis" <mark.davis at jtcsv.com>
    Message-ID:  <005301c56a2f$ca8a36f0$6501a8c0 at sanjose.ibm.com>

  | > Are you also going to declare that New York can't use EST?
  | No. I don't see how what I said would give you that impression.

But "EST" is ambiguous, how can you possibly use it for your purposes?

Aside from the (several) different meanings in north America, it's also
the name of (both) the summer and standard timezones in eastern
Australia (all 4 (or is it more) different versions of them).

The first thing that you should note is that you do not need to distinguish
(in user input) the difference between summer and standard timezones,
you can always work that out from the date, assuming you know the locality.

People use either "local time" (either the local time where they are,
which is most common, or sometimes "local time at location X"), or they
use UTC (whether they call it that or GMT).   No-one expresses the time
in terms of what it would be if only it was not summer right now, or if
summer time didn't apply.    Similarly, a meeting at 4pm every Monday
is at 4pm standard time in winter, and 4pm summer time in summer, whether
the meeting schedule was set in summer or winter.

Second, the only half way reliable way to work out what time zone applies
is to find out what location the time is supposed to apply in, that is,
if someone wants to schedule a meeting at 4pm, you need to know 4pm in
which city.    Given that there's no longer any ambiguity at all, and just
a combination of programming, and database, to convert to universal time
so it can be shared with others (and represented in whatever timezone is
convenient for them, which should either be in numeric form (+1000, -0700,
or something) or in terms of a location.

Asking for any form of time zone name input is just asking for trouble.
Outputting one where you intend its use to be anything more than a
comfort blanket for the user is just plain silly.

Even as just friendly info, zone names help rather than hinder only in
those locations (countries really, though Europe might count as a country
for this) where there are multiple timezones - in others, the time is just
the time, and has no name at all.


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