[tz] What data should TZDB offer?

Stephen Colebourne scolebourne at joda.org
Mon Jun 7 14:38:37 UTC 2021

On Mon, 7 Jun 2021 at 10:28, Guy Harris via tz <tz at iana.org> wrote:
> Note that theory.html says "don't do that":
>         In short, many, perhaps most, of the tz database's pre-1970 and future timestamps are either wrong or misleading. Any attempt to pass the tz database off as the definition of time should be unacceptable to anybody who cares about the facts. In particular, the tz database's LMT offsets should not be considered meaningful, and should not prompt creation of timezones merely because two locations differ in LMT or transitioned to standard time at different dates.

If you ask a Java library "what was the offset on 1st Jan 1600 at
12:36 pm" they will all provide an answer. My understanding is that
the same is true of libraries in many other environments. Most systems
will provide LMT as the answer. Some (eg. the older Java API) will
provide a non-LMT offset. Those of us on this list know that the
question being asked is pretty stupid, but it is asked by end users.
And when it is asked, people are surprised by the LMT answer. I is
worthwhile considering if LMT is the best solution to the far past

The second point is not relevant - the proposal is to determine which
zones get a LMT and history based on post-1970 data with an ISO
country minimum. There is no proposal to create timezones solely for


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