[tz] Preparing to fork tzdb

Clive D.W. Feather clive at davros.org
Thu Sep 23 12:29:33 UTC 2021

Howard Hinnant via tz said:
> > A primary goal of the recent patches was to avoid racial or national preferences that were present in the previous setup.
> I applaud the motivation to make these changes.  But is it really ethical to knowingly introduce incorrect information into the default configuration, where previously the information was correct?  Even if said information is ???historic??? or even ???not officially supported????

My understanding of the default setup is:
* If two places had different times at any point since 1970, they must have
separate zones.
* If two places had the same time at all points since 1970, they do not
have to have the same zone even if they differed before 1970.
* The data for a zone applies to the whole zone for times after 1970, but
might only apply to part of the zone before 1970.

That might not be the best arrangement but, if I'm understanding correctly,
it's what we've got.

Based on that, then an alien observer would say that the area currently
covered by the nation-states of Germany, Norway, and Sweden is allowed to
be a single zone. And, if we were creating the TZDB from new right now,
then under those rules plus the desire to minimize the number of zones,
they would be a single zone. The data in them is *not* incorrect; it meets
the policy described above.

Therefore any argument that they should be two or three zones instead needs
to be based on some *other* objective requirement. Which, I suspect, needs
to be *added* to the present policies rather than just handwaved. Such
requirements could be:
* Never abolish a zone once it's got into the default setup.
* At least one zone per 3166 "country".
* At least one zone per "authority".
* Use separate zones if we have reliable data going back to 1945 (or pick
some other year).

Clive D.W. Feather          | If you lie to the compiler,
Email: clive at davros.org     | it will get its revenge.
Web: http://www.davros.org  |   - Henry Spencer
Mobile: +44 7973 377646

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