Time Zone Localizations

Mark Davis mark.davis at jtcsv.com
Mon Jun 14 04:17:24 UTC 2004

comments below.

► शिष्यादिच्छेत्पराजयम् ◄

----- Original Message ----- 
From: "John Cowan" <cowan at ccil.org>
To: "Mark Davis" <mark.davis at jtcsv.com>
Cc: "David Keegel" <djk at cybersource.com.au>; "Paul Eggert" <eggert at CS.UCLA.EDU>;
<tz at lecserver.nci.nih.gov>
Sent: Sun, 2004 Jun 13 18:30
Subject: Re: Time Zone Localizations

> Mark Davis scripsit:
> > 3. What is the meaning of an TZID
> Just what is the meaning of "meaning" in this context?

A TZID is not just a sequence of letters, it has a meaning. That meaning appears
to be explained in Threory, but your comments below make me very nervous.

> > 4. What is the versioning scheme, including assurance that:
> >     - once a version is issued it is never changed.
> >     - TZIDs are stable, in the sense that they will never be withdrawn
> >       or reused with a substantially different semantic in later versions
> Again, what does that mean?  New York might move to a new timezone,
> if Congress so decided, or if it became an independent country (hey,
> we pay them more than they pay us).  In that case the Eastern zone would
> have to be renamed America/Philadelphia, or whatever.

This is exactly the kind of thing that needs to be made clear, exactly what
needs to be specified by the "meaning". There are at least two choices:

1. America/New_York will always be the timezone for the city of New York, even
if it secedes from the US, joins Canada, and goes on Newfoundland time.

2. America/New_York is a stand-in for US Eastern Time. If New York City secedes
and changes, the America/New_York TZID will associated with US Eastern Time.

Of course, that may be unlikely for NYC, but the principle has to be clear so
that its application to other TZIDs is well-defined.

> More probably, Congress might change the DST rules, in which case the
> current predictions of the U.S. zones would become incorrect and would
> have to be updated.
> The only other conceivable scenario would be for the Big Apple to have
> its name changed (Nueva York might be a possibility).  In that case, some
> other New York might come to prominence such that it became the largest
> city in some other time zone in the Americas.  That's not very likely,
> but it would constitute a genuine reuse.

And if America/New_York is to be stable, that would, of course, be a huge
mistake, akin to changing CS from Czechoslovakia to Serbia and Montenegro.
Simply because the city were renamed should have no effect on the TZID. If it
were necessary to have another city because, essentially, the zone that was
associated with NYC needs to be split, that is another matter. One would expect
a new TZID to be introduced in that case.

> The advantage and disadvantage of Olson TZIDs is that they aren't
> arbitrary: they depend entirely on facts on the ground.

That is a bit too facile. They don't depend entirely on the facts on the ground;
they have to have a clear meaning so that when the "facts on ground" change, one
can have reasonable expectations as to what principles would be maintained in
adjusting the TZIDs to the new circumstances.

> -- 
> John Cowan   jcowan at reutershealth.com   http://www.reutershealth.com
>     "Mr. Lane, if you ever wish anything that I can do, all you will have
>         to do will be to send me a telegram asking and it will be done."
>     "Mr. Hearst, if you ever get a telegram from me asking you to do
>         anything, you can put the telegram down as a forgery."

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