[tz] What data should TZDB offer?

Clive D.W. Feather clive at davros.org
Mon Jun 7 09:07:05 UTC 2021

Stephen Colebourne via tz said:
> 1) LMT
> LMT is confusing for many downstream users because they don't
> understand the concept.

In that case, explain it better. But just because people don't understand
how the real world worked is not a good reason to lie to them

> Recent threads have noted queries from
> Postgres users, I can attest to confusion in various Java libraries.
> In fact, earlier versions of Java removed the LMT concept. I think the
> time is right to properly consider an alternative to LMT. I believe we
> can define an offset for each region that the region has most
> typically been associated with post 1970. For example, Europe/Paris is
> most associated with +01:00 since 1970. This provides the "normal
> looking" offset that most users desire for the LMT period.

Derick has pointed out that this looks ridiculous for Amsterdam. I'll also
point out Dublin, where the official time was Dublin Mean Time for many
years. Making TZDB say that Dublin used GMT before it used DMT is total and
absolute nonsense.

I thought you were the one objecting violently to the idea that a zone
might contain fake data; wasn't that the whole point of your Stockholm
argument? So why do you want to create fake data now?

If LMT is what happened, then LMT is what the database should say. If
people don't want to see LMT in their systems, delete everything before
1970 in your local copy.

> Proposal
> ------------
> That TZDB shall adopt the principle that the main geographic files
> (africa to southamerica) shall contain data with full history for
> locations where zone history has differed since 1970 subject to the
> minimum requirement that there is at least one full zone with history
> defined for each independent country as defined by ISO-3166-1.

I disagree with this. There is no need to create zones just to have one per

> Dependent territories in ISO-3166-1 that are within 1/24th of the
> earth circumference of another dependent territory or parent country
> with the same sovereignty shall be combined if their post-1970 history
> is identical.

I also disagree with this. If it's justified to have separate zones for
countries, why not for dependent territories? And why should the distance

Oh, and why on earth "1/24th" instead of "15 degrees" like everyone is used
to? And which circumference? The earth has more than one. Why not just give
a distance in km? And why treat a territory 10 degrees due south
differently to one 20 degrees due south?

Are you measuring from the nearest points of the two territories and, if so,
are you working from high tide, low tide, 3 mile limit, 15 mile limit,
50 mile limit, or claimed waters? Or are you measuring from a capital city
or other administrative centre? What if the dependent territory is not
north or south of the administrative centre of the country but some other
part of it?

Oh, please define "dependent".

This is a useless definition as written.

Why are you happy for Taiwan to be excluded under these rules but not
Sweden? Answer: politics, which is what we are trying to avoid.

For the record, I OBJECT to this proposal.

> That TZDB shall replace LMT with the offset that best represents
> standard time for the location during the period 1970 to 2021.

For the record, I OBJECT to this proposal.

> It is my belief that this proposal meets the issues expressed above
> while also respecting the concerns of fairness, guidelines and
> politics expressed by others. For example, TZDB would not include a
> full zone with history for Kosovo until ISO-3166-1 includes it. This
> provides a straightforward defence against the worst issues of
> politics.

Better would be to ignore politics entirely and say that TZDB would not
include a zone for Kosovo until its time differs from wherever is used now.

> The dependent territory rules are designed to allow locations that are
> close to each other in distance and sovereignty to be combined, such
> as  Jersey and London.

Jersey is not part of the UK - it is a Crown Dependency. Not the same thing
at all.

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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