proposed time zone package changes
Dave at Cantor.mv.com
Mon Jul 13 13:35:51 UTC 2009
On 13-Jul-2009, Robert Elz wrote:
From: Robert Elz <kre at munnari.OZ.AU>
Date sent: Mon, 13 Jul 2009 16:54:56 +0700
> Date: Sat, 11 Jul 2009 14:07:35 -0400
> From: "Dave Cantor" <Dave at Cantor.mv.com>
> Message-ID: <4A58D4E7.20949.B6C0C36 at Dave.Cantor.mv.com>
> | I disagree with this. When a region does not observe DST at all,
> | the POSIX string simply indicates its abbreviation and offset,
> | e.g. UTC0 or EST5. When a region observes DST all year, it's
> | the same as observing the standard time of the next time zone
> | eastward all year. In my opinion, it should simply be coded
> | that way.
> As I understand it, the issue is to deal with regions with time zone
> specifications that cover things that POSIX strings cannot represent.
> That is neither regions that have no summer time, nor regions that
> have "summer time all year" (ie: are not in the time zone that would be
> logically appropriate, I assume).
> I'm no expert on POSIX strings, but I think the example that caused
> the problem was a region that switched summer time on, but never
> switched it off again - that is (so we were told, and I am willing to
> accept without evidence to the contrrary) something that POSIX strings
> just do not handle.
> Of course, this time, the "never switched it off" is just our way of
> currently encoding "no-one has yet even hinted at the end date, so we
> have no idea what to put", which is why the other half of ado's proposed
> fix was just to stick an arbitrary end date on Dhaka's summer time, so the
> problem case goes away for people who don't have the other fix).
> After all this, I'm not sure what you're objecting to? There are two
> relevant (proposed) changes - one to just not include a POSIX string when
> it is impossible to make a valid one (if you object to that, why? And what
> would your alternative be - including invalid strings isn't useful for
> anyone.) The other is the arbitrary end date for summer time for Dhaka
> (Bangladesh) - that one makes me a little queasy, but I'm not sure what
> else to do to handle people who have old implementations of zic, and so
> can't get the benefit of the former fix. If your objection was to
> picking an arbitrary date, then is it better to leave those people with
> compiled files with invalidly formatted data? Or, if the objection is
> just to the date picked, suggest a better one - we can probably do
> better than "the end of the year" as a guess, though the closer we come
> to reasonable the more likely it is that someone will believe that our
> arbitrary guess is actually based upon some reliable data. The one time
> that you can be pretty much sure that no-one, however stupid the politicians
> are, is ever going to pick to end summer time is midnight, local time,
> new year's eve (ie: 00:00 Jan 1) - as no-one is going to want to deal
> with what it means (or the cost of fireworks) with having two year
> ends occurring just an hour apart...
What I'm objecting to is not generating a POSIX-style TZ string
when it is possible to do so. It seems to me that the string
"XDT-2" would be a workable TZ string for an exemplary fictitious
location Fictitious/Xyzzy located 1 hour east of UTC, but using a
time 2 hours east of UTC all year.
Maybe I'm missing some key point (other than that POSIX TZ
strings are insufficient for expressing all the rules that
political entities actually enact).
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