[tz] tzdb timezone names/identifiers and links (was: Add new timezone for Hanoi Capital, Vietnam)

Hans-Joerg Happel happel at audriga.com
Wed Feb 20 16:40:03 UTC 2019

This is basically what I was about when asking for the "scope" of tzdb,
and might end up in a similar discussion concerning timezone ids just
like the Wikipedia's inclusionism/exclusionism debate.


a) (Exclusionist) Timezone ids should be kept at a minimum level
required to model tz rules appropriately
b) (Inclusionist) There should be at least one timezone id for each ISO
3166-1 TLC
...and as the "Hanoi" case would not be covered by (b) the even extended
inclusionist approach would rather be something like:
c) (Inclusionist+) There should be at least one timezone id for each
"timezone" (in the sense of tzdb's consistent-since-1970 definition) for
each ISO 3166-1 TLC

I see the point of simply sticking to (a). However, not all all users of
tzdb will grasp this, and so there will always be considerable "misuse"
of timezone ids and discussions such as the recent "Hanoi" thread.

However it looks like there is no real solution to this, as either
choice has its subtleties. So sticking to the status quo might be the
best to do for now.

While I think I understand the perspective of people who are arguing to
focus on core tzdb maintenance, I'd however encourage tzdb "users"
(which I guess are also represented on this list) to speak up regarding
challenges they observe.

I think such discussion might be worthwhile 1) to raise sensitivity for
tzdb usage challenges in this community and 2) to better understand pain
points in the usage of time zones / time zone identifiers in general.

For instance, has anybody ever seen an approach such as advised in the
note suggested by Paul [1], or are we actually all sticking to just
storing  tzdb identifiers?

Thanks and best,


Timezone boundaries are not part of the stable interface.
For example, even though the <samp>Asia/Bangkok</samp> timezone
currently includes Chang Mai, Hanoi, and Phnom Penh, this is not part
of the stable interface and the timezone can split at any time.
If a calendar application records a future event in some location other
than Bangkok by putting "<samp>Asia/Bangkok</samp>" in the event's record,
the application should be robust in the presence of timezone splits
between now and the future time.

On 20.02.19 13:37, Stephen Colebourne wrote:
> I strongly oppose this patch. At least one zone per ISO 3166-1 is a
> vital part of this project and an entirely sensible rule. It is what
> users expect the project to provide.
> TZDB identifiers are used incredibly widely, and are seen on many
> public-facing systems. I understand that is not seen as desirable by
> some here, but it is the truth. When a country splits, it is usually
> for painful reasons. The idea that the half of the country should be
> forced to use the old identifier simply isn't tenable.
> Stephen
> On Tue, 19 Feb 2019 at 23:17, Paul Eggert <eggert at cs.ucla.edu> wrote:
>> On 2/19/19 2:31 PM, Tim Parenti wrote:
>>> So, since it's pretty clear that the "There should typically be at
>>> least one name for each ISO 3166-1 officially assigned two-letter code
>>> for an inhabited country or territory" guideline has been, if not
>>> abandoned entirely, at least significantly de-prioritized, perhaps
>>> theory.html needs an update indicating that, yes, this /used/ to be
>>> considered more important, but is not any longer (perhaps going a bit
>>> into the rationale), and that we don't intend to create new zones
>>> anymore if that's the only justification.
>> Sounds good to me; proposed patch attached.

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