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TimeZones and politics Re: How to tell (in advance) if a date-timeis ambiguous?

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From:
Bill Ricker
Date:
July 11, 2017 18:50
Subject:
TimeZones and politics Re: How to tell (in advance) if a date-timeis ambiguous?
Message ID:
CAAbKA3Xg+m6XAkv+yww9dmiPUZp9_ncYe5jYtmbdQqAR0_09pQ@mail.gmail.com
On Tue, Jul 11, 2017 at 4:07 AM, Binarus <lists@binarus.de> wrote:
>
> On 10.07.2017 20:14, Eric Brine wrote:
> > I don't understand the conditions. The law determines when the switching
> > of offsets from UTC happen, not some person. The switch doesn't happen
> > at 08:48:27 am in Chicago; it happens at 2am.
>
> This point of view is a bit U.S. centric. Indeed, you are describing how
> it *should* be, but

We tend to use the timezone nearest us for examples because we're less
likely to be wrong and thence get dragged into discussing the example
instead of the concept.

> 1) The timezone database is updated several times a year, and that
> surely has its reason. Obviously, laws are changing (a part of them very
> surprisingly and fast),

Oh yes. This is indeed why.

The TZ info file is interesting only because it is worldwide and political.

>  and the next law could determine the switch to
> happen at 08:48:27 am, and

It could in theory, but would be beyond atypical.
(Why? Perhaps a(n) hereditary national leader wants to honor the
moment of his father's birth?)
(The file format and software should handle  08:48,not sure about 08:48:27 ?)

In practice, the only odd-seconds-level transitions are the positive
or negative leap second insertion, which are even weirder when you
think too hard than the (typically) hour added and removed in DST.
    (At leap-second, there is a minute with either 59 or 61 seconds,
so there are times legal then that aren't elsewhen, or a single second
that is illegal then. Most software just continues to say :59 for an
additional second to avoid messing up downstream software that thinks
23:59:60 GMT is syntactically illegal even though on certain on 12-31
and 06-30 when mandated it should be semantically Legal. Worse, unlike
TZ DST, it occurs simultaneously world wide and so may be during the
business day in Oceania and East Asia, even of the half or quarter
hour in those odd offset TZs. The ambiguous hour during DST->ST
rollback and the illegal hour vanished at ST->DST roll forward are
semantically illegal but syntactically legal. Which allows them to
propagate further before something chokes. )

> 2) Laws are made by persons, in some cases by a single person. For
> example, in 2007, Venezuela's president Hugo Chavez moved Venezuela's
> time zone by 30 minutes backwards without any real reason, but just as a
> political statement, putting the country in a half-hour time zone. This
> shows that weird things can happen to time zones at all times and very
> surprisingly.

Indeed.
    I try not to use such eccentric examples to avoid dragging
politics into a technical discussion, but yes, most of the urgent
updates are results of small-country power-politics and/or equally
political regional re-alignments. Large democracies tend to plan their
changes well in advance, e.g. USA 2007, we had plenty of warning; the
question was if IT had updated production systems adequately.
(Shocking Answer: No.)
  Hence i only _reluctantly_ used the March update adding Haiti to EDT
2017 at the last minute to demonstrate short notice.
    (I haven't looked up news stories but infer restoring EDT
indicates a milestone in their infrastructure's hurricane recovery; if
so, congratulations.)

(  I'm hoping with New England states debating laws that make
switching TZ conditional on adjacent states doing likewise we don't
have a last minute vote in e.g. NH triggering Maine & Mass & NH all
flipping on short notice ... but it could happen... but it's still
hypothetical, so a weaker example.)

> Thus, when developing an application targeted to audience all over the
> world, you can't rely on what you know about your own country.

Absolutely.
Everyone who has been in the TZ data knows this.
We work on this TZ software because we are crazy enough to care about
these edgecases.

But we'll still typically use our own TZ for our DST examples because
it's embarrassing and derailing to get e.g. Haiti's DST transition
wrong in an email example.

(And then instead of US-centrism we'd be called worse things for
talking-down to a small country _and_ being wrong simultaneously.)

Do please feel free to use your TZ (or others you know well( in your examples !

But don't expect us to be shocked by Venezualan TZ mandates; only the
short notice made it more eccentric than other isolated half hour
zones e.g.Newfoundland's UTC-03:30/-02:30. Large expanses of on half
offset in South Asia and Australia may serve a purpose, but I can't
explain it.

But AFAIK all TZs to-date that are actually TZs (as in, not Local Mean
Time, the evil that TZs fixed for the 19thC steam & telegraph Railroad
schedules) have been at no finer than quarter hour offset from
GMT/UTC, and mostly hour offsets, with some rather famous half-hours
(India, Australia) and infamous (Venezuela).
    The quarter-hour offsets are peculiar and one can only ask "Why?"
yet always is a Why.  Kathmandu's UTC+05:45 maybe the strangest but is
still intensely geo-political -- splitting the difference between two
powerful neighbors,China/Tibet +06 and India(Kolkata) +05:30. Picking
either could anger the other neighbor, so split the difference.

Yes, it's political.
But to us here, the output of the political process is our input data
We try to make things behave as humans will expect according to their
Quartz Timex  or iPhone Clock app.


-- 
Bill Ricker
bill.n1vux@gmail.com
https://www.linkedin.com/in/n1vux

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