[tz] Preparing to fork tzdb

Brooks Harris brooks at edlmax.com
Wed Sep 22 18:32:01 UTC 2021

On 2021-09-22 9:17 AM, Eliot Lear via tz wrote:
> On 22.09.21 15:09, dpatte via tz wrote:
>> Iso is a living international standard, and it's their mandate, not 
>> the mandate of timezone collectors to do the negotiation and 
>> diplomacy in order to arrive at and maintain the world standard.
> Right.  And this group has avoided their business for decades.
I agree. There should be only one 'authority' for country codes, and ISO 
3166 is it as far as I know.

It seems it is the mapping of the country codes to time zone names 
(tags) that is causing the current difficulties. It seems to me it 
should not be such a problem. As zone1970.tab (and zone.tab) says:

# This table is intended as an aid for users, to help them select timezones
# appropriate for their practical needs.  It is not intended to take or
# endorse any position on legal or territorial claims.

It is useful for "practical needs" but cannot be relied upon in all 
circumstances. Tzdb can use ISO 3166 but should not alter it or fall 
victim to any political controversies it might imply.

I would point out, however, that zone1970.tab also contains the time 
zone *coordinates*. This is different matter than country codes. In the 
work I'm doing the coordinates are important. They define the 
approximate default coordinates of time zones, and this is useful in a 
number of ways, indicating geographic distances between time zones and 
distinction of Northern and Southern hemispheres.

I think this has significance to the 'merging' controversy. 
"Europe/Oslo" is not the same time zone as "Europe/Berlin". They may 
have been using the same rule sets since 1970 resulting in identical 
local YMDhms representations but they have different time zone names 
(tags) and distinct coordinates. Oslo is not the same city as Berlin. If 
time zone "Europe/Oslo" ever existed it still exists today. 
"Europe/Oslo" could adopt a new set of rules different from 
"Europe/Berlin" and its possible they might given the new elective rules 
being suggested by the EU.

Olsen's original insight to use towns and cities to name time zones 
turns out to be extraordinarily useful. Whether or not "Europe/Oslo" is 
in Norway is entirely beside the point of local time in the 
"Europe/Oslo" time zone. Time zones really exist only in the time domain 
relative to the (special) "Etc/UTC" time zone. I'm sure most 
contributors to the tz list understand this, but there's a natural 
tendency equate a time zone with a location or place since this is where 
the general idea comes from to begin with. But I think tzdb must be 
vigilant to maintain this conceptual separation of time zone v.s. 
"place", especially in regard to politically named and claimed 
geographic boundaries such as Norway or Germany.

This separation of "time" from "place" may seem inconsistent with my 
previous point about time zone coordinates but I don't think so. The 
time zone names are based on cities and the cities have approximate 
geographical location and this ties the time zone to a location. This is 
useful for some important purposes and supports the basic idea behind 
time zones. But it is a separate conceptual and implementation 
consideration from the local time zone YMDhms representation with 
respect to "Etc/UTC". The geographic coordinates have nothing to do with 
the local time because any time zone may adopt any UTC-offset (STDOFF) 
or DST rules they choose and this decouples the time zone's local time 
from the city location.

I'm sure most tzdb experts recognize this distinction but it seems to 
have somehow been lost track of recently. I hope participants can find 
the way back to the cooperation that has characterized the group for so 


-Brooks Harris

More information about the tz mailing list