[tz] [PROPOSED] Avoid backward links in zone.tab
Paul Eggert
eggert at cs.ucla.edu
Tue May 11 18:03:57 UTC 2021
On 5/11/21 5:32 AM, Michael H Deckers wrote:
> Rather, the corresponding geographic coordinates in zone.tab
> are no longer connected with the timezone name, only with
> an ISO country code.
I wouldn't put it that way. In zone.tab, a line's geographic coordinates
are connected with both the country code and the timezone name. That is,
the coordinates identify a location that is both (a) in the country, and
(b) has clocks that have agreed with the timezone since 1970.
> The same holds for several proposed lines
> in zone1070.tab such as
> AQ,KW,SA,YE +2438+04643 Etc/GMT-3 Arabia, Syowa
> What are these geographical coordinates supposed to indicate?
They indicate a major location within the designated area. This is the
same as the non-Etc lines in zone1970.tab, and it's the same role they
play in zone.tab.
> One of the successful design choices of the tzdb
> database was to identify timezones by locations (rather than
> by areas or countries), so that location names and location
> coordinates are equivalent means of identifying timezones
> of locations. Is this still true?
That depends on what one means by "equivalent" :-). Timezone names like
Etc/GMT never identified single locations all that well.
An alternative strategy to what's proposed in the patch, is to keep a
single location-based Zone in place of each Etc/* name that the patch
uses. For example, where the patch proposes making several names
(Asia/Dubai, Asia/Muscat, Indian/Mahe, Indian/Reunion)
backward-compatibility aliases for Etc/GMT-4, we could instead keep
Asia/Dubai (the most-populous location) as a Zone, and have the other
names be backward-compatibility aliases for Asia/Dubai.
In the long run this approach would be a bit more work than what the
patch proposes, as it'd mean we should continue to maintain out-of-scope
(pre-1970) data for Asia/Dubai, Asia/Bangkok, etc. The main advantage of
it would be avoiding Etc/* names as link targets and in zone*.tab files.
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