[tz] TZDB use cases

Guy Harris gharris at sonic.net
Sun Oct 3 17:32:25 UTC 2021

On Oct 3, 2021, at 2:47 AM, Stephen Colebourne via tz <tz at iana.org> wrote:

> 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:
> https://www.sec.gov/Archives/edgar/data/1308106/000119312512368196/d401408dex21.htm
> "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"


"Base Rate means for any Loan or Unpaid Sum in EUR the EURIBOR Screen Rate as at 11.00 a.m. (Frankfurt time), on the relevant Rate Fixing Day for such currency for a period equal in length to the Interest Period of that Loan or Unpaid Sum and, if any such rate is below zero, the Base Rate will be deemed to be zero."


	# This is a directory into which the 2021a lz-compressed tarball was unpacked
	# We look for a tzid corresponding to Oslo in a source file
	$ egrep '/Oslo' * | egrep -v 'backzone|to2050.tzs|tzdata.zi|zone.tab|zone1970.tab'
	backward:Link	Europe/Oslo		Atlantic/Jan_Mayen
	europe:Zone	Europe/Oslo	0:43:00 -	LMT	1895 Jan  1
	europe:# All these events predate our cutoff date of 1970, so use Europe/Oslo
	europe:Link	Europe/Oslo	Arctic/Longyearbyen
	# There is one.
	# Now we look for a tzid corresponding to Frankfurt in a source file
	$ egrep '/Frankfurt' * | egrep -v 'backzone|to2050.tzs|tzdata.zi|zone.tab|zone1970.tab'
	# There isn't one.

> 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
> Oslo.
> 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.

So what do those applications due for contracts that refer to "Frankfurt time"?

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