[tz] TZDB use cases

Stephen Colebourne scolebourne at joda.org
Sun Oct 3 09:47:02 UTC 2021

On Sun, 3 Oct 2021 at 00:29, Guy Harris via tz <tz at iana.org> wrote:
> So it's not as if there was an *inherent* need for Europe/Oslo as a tzdb ID to make these applications work; if there had never been a Europe/Oslo ID, and Norwegian locations had used Europe/Berlin, that would have been sufficient to, for example, record future events taking place in Norway.

Here is a not untypical legal contract:
"NIBOR means that the rate for an interest period will be the rate for
deposits in Norwegian Kroner for a period as defined under Bond
Reference Rate which appears on the Reuters Screen NIBR Page as of
12.00 noon, Oslo time"

The 100% correct way to represent this in a business application is to
define an ID scheme that includes an ID for "Oslo time" and then keep
a constantly updated mapping from that ID to the actual zone used in

In practice, most business applications/companies would find that very
expensive and cumbersome to maintain by themselves. Instead, most
business applications simply use "Europe/Oslo" to represent the
concept. Effectively, this outsources both the ID and the upkeep of
the mapping to tzdb.

Feel free to say that the business applications are doing it wrong.
Feel free to say that this shouldn't be tzdb's issue to solve. But my
answer will be the same - that no longer matters because this *is* how
tzdb IDs are actually used. And in practice it has worked pretty
effectively for many years across much of the planet.

And IMO, if tzdb had never published an ID for Oslo, somebody
somewhere would have had to invent such a thing - either internal
inside lots of companies, or a separate non-tzdb open source project.
ie. that there is an inherent need is demonstrated by actual usage.


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