[tz] [PATCH 0/2] Follow Australian common usage and update CST/CST to CST/CDT and EST/EST to EST/EDT etc [SEC=UNCLASSIFIED]

Dennis Ferguson dennis.c.ferguson at gmail.com
Thu Apr 11 16:53:08 UTC 2013

On 10 Apr, 2013, at 19:04 , Peter Stagg <P.Stagg at bom.gov.au> wrote:
> Only tree of the four states in the "Eastern Standard Timezone" have daylight savings and they only have it for aprox. four of the twelve months in the year. And as someone pointed out before many web sites unwittingly use the TZ Database data to automatically timestamp pages. So the frequency of  use of "EST" is destined to be much higher then "EDT" and therefore the search is meaningless.

I have no particular interest in what Australian time zone abbreviations
should have been, or should be going forward, but I'm a bit interested
in the topic mentioned above.  If I needed to interpret a timestamp recorded
by sites which "unwittingly use" the TZ database the TZ database itself
makes it clear what I would need to know to disambiguate it: I need to know
where in Australia the timestamp was taken (and I need to hope the timestamp
wasn't taken in the 2 hours per year which can't be disambiguated, though
the TZ database does also tell me which 2 hours are unavoidably ambiguous).
I understand the effect of the change proposed is to reduce the information
I need to know to disambiguate future timestamps recorded via unwitting
use of the TZ database to "Australia", and this seems useful to me independent
of what terms people in Australia actually use (or used) to describe the
the current time on their clocks.

I would note, however, that the proposed patch doesn't just limit itself
to reducing the ambiguity of future timestamps not yet recorded, it also
changes the database information about the abbreviations used for historical
timestamps produced by the TZ database.  While the issue of what time zone
abbreviations people in Australia might have preferred to use is for others
to debate there can be no dispute about the abbreviations the TZ database
has used for the last 20 years, nor is there any way to change that, but
by altering that data one is effectively removing the information about the
history of the database itself that one would need to know to interpret
timestamps already recorded with the "unwitting use" of the TZ database.

Is there a reason to change the historical TZ database abbreviations
rather than just making a change which is applied going forward?  You
can't really fix what has already happened, and attempting to pretend
that it didn't happen that way just seems to increase the ambiguities that
people with a need to interpret old timestamps produced with old versions
of the TZ database need to deal with while having no offsetting advantages
that I can see.

As a policy matter I'd prefer that the bar to changing past TZ database
data was set much higher (i.e. should require evidence of factual errors
rather than just issues of opinion) than the bar to making changes which
only effect the future.

Dennis Ferguson

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