[tz] TZDB use cases
gharris at sonic.net
Tue Oct 5 07:27:07 UTC 2021
On Oct 4, 2021, at 4:00 PM, Stephen Colebourne via tz <tz at iana.org> wrote:
> On Sun, 3 Oct 2021 at 12:53, Eliot Lear via tz <tz at iana.org> wrote:
>> For another, the same sort of contract could be
>> made for Piscataway, NJ, or Niemes. Fr, for which there are no specific
>> TZ definitions.
> And Guy asks
>> So what do those applications due for contracts that refer to "Frankfurt time"?
> So, it turns out that there is, I believe, a critical difference here
> between the US view of timezones and the European one. In the US,
> timezones do not follow the boundary of the whole country, nor even
Canada, Australia, Russia, and Brazil, possibly among others, say "hi!"
The world does not consist solely of "the United States" and "Europe". (And part of Russia is in Europe - and it has at least two European tzdb regions, Europe/Kaliningrad and Europe/Moscow.)
> In Europe, by contrast, timezone boundaries are very much
> driven by country boundaries.
Except where they aren't.
> Thus the answer for Frankfurt is that applications use the zone ID
> associated with the country, Europe/Berlin,
So those applications have some mechanism to map "Frankfurt" to "Europe/Berlin".
*If* that mechanism maps "Frankfurt" to "Germany" and then maps "Germany" to "Europe/Berlin", that works... for Europe. There are places where it won't work.
> and applications accept
> that this is not actually "Frankfurt Time", but a good enough
> approximation. (Same with Nimes and Europe/Paris). Because there are a
> limited set of countries, which (almost) all have an associated tz ID
> and zone rules only change at the country-level, this works out just
So applications that use a mechanism as described above for countries outside (Western) Europe will not work in Canada:
"the rate of interest per annum equal to the average annual yield rate for one month Canadian Dollar bankers’ acceptances (expressed for such purpose as a yearly rate per annum in accordance with Section 5.4) which rate is shown on the display referred to as the “CDOR Page” (or any display substituted therefor) of Reuters Limited (or any successor thereto or Affiliate thereof) at 10:00 a.m. (Toronto time) on such day or, if such day is not a Banking Day, on the immediately preceding Banking Day, plus 1.00% per annum,"
"1.1.20 "Bankers' Acceptance Discount Rate" means (i) in respect of Bankers' Acceptances to be purchased by the Lenders which are Schedule I banks under the Bank Act (Canada), the average rate for Canadian Dollar bankers' acceptances having Designated Periods of 1, 2, 3 or 6 months quoted on Reuters Service, page CDOR "Canadian Interbank Bid BA Rates" (the "CDOR Rate"), having an identical Designated Period to that of the Bankers' Acceptance to be issued on such day, (ii) in respect of Bankers' Acceptances to be purchased by the Lenders which are Schedule II banks under the Bank Act (Canada) or Schedule III banks under the Bank Act (Canada) which are not subject to the restrictions and requirements referred to in Section 524(2) thereof and in respect of Discount Notes, the rate for Canadian Dollar bankers' acceptances quoted by the BA Schedule II Reference Lender, having an identical Designated Period to that of the Bankers' Acceptance to be issued on such day, and (iii) in respect of Discount Notes to be purchased by Caisse centrale Desjardins, the annual discount rate established by Caisse centrale Desjardins in accordance with its normal practice as corresponding to the "all-in cost", expressed as a rate per annum and calculated at approximately 10:00 a.m. (Montreal time) on the date of issue of such Discount Notes, to Caisse centrale Desjardins to provide fixed rate loans denominated in Canadian Dollars to be made for a comparable term as that for which such Discount Notes are to be issued and in an amount approximately equal to the face value of the Discount Notes to be then issued by Caisse centrale Desjardins as a part of such issue; the whole having regard to the costs and charges to Caisse centrale Desjardins in obtaining matching deposits in Canadian Dollars in an amount sufficient to fund such fixed rate loans and for a comparable term, together with all other costs and charges (other than internal costs and charges) incidental thereto including the imputed costs of any primary, secondary or other reserves or special deposits required to be maintained in the circumstances; provided that the rates referred to in clauses (ii) and (iii) above may not exceed the rate determined under paragraph (i) by more than 10 basis points (.10%) (in each of cases (i), (ii) and (iii), the "Discount Rates"). In all cases, the Discount Rates shall be quoted at approximately 10:00 A.M. (Montreal time) on the Acceptance Date calculated on the basis of a year of 365 days."
""Expiry Time" means the earlier of:
(i) 4:30 p.m. (Vancouver time) on the Due Date; and
(ii) 4:30 p.m. (Vancouver time) on the fifth Business Day after the Qualification Date;"
"BBSY Rate for a period means the higher of zero and the following rate determined at or about 11.00am (Sydney time) on the first day of that period (or if different the time specified by the Facility Agent as the time at which this rate is normally published) and for a period equivalent (in the opinion of the Facility Agent, without the need for instructions) to the Interest Period:"
"unless a contrary indication appears, a time of day is a reference to Melbourne time."
"(TIME OF DAY) a reference to time is a reference to Perth time;"
or the US:
"Each Advance under the Revolving Credit Loan (each, a ‘Borrowing’) shall be made on notice, given not later than 12:00 Noon (New York time) on the third Business Day prior to the date of the proposed Borrowing in the case of a LIBOR Rate Advance, and not later than 12:00 Noon (New York time) on the date of the proposed Borrowing in the case of a Base Rate Advance, by Borrower to Lender. Unless otherwise agreed in writing by Lender, each such notice of a Borrowing shall be by telephone, confirmed immediately in writing (by telecopier, e-mail or otherwise as permitted hereunder), substantially in the form of Exhibit C (a ‘Notice of Borrowing’), specifying therein the requested (i) date of such Borrowing, (ii) Type of Advance comprising such Borrowing, (iii) aggregate principal amount of such Borrowing, and (iv) the Interest Period, in the case of a LIBOR Rate Advance. Each Borrowing (including any Conversion or Continuation) shall be in an amount equal to One Million Dollars ($1,000,000) or a whole multiple of Five Hundred Thousand Dollars ($500,000) in excess thereof."
"1.6 Time References. Unless the context of this Agreement or any other Loan Document clearly requires otherwise, all references to time of day refer to Pacific standard time or Pacific daylight saving time, as in effect in Los Angeles, California on such day. ..."
"“Eleventh District Cost of Funds Rate” means, with respect to any Interest Determination Date specified below (an “Eleventh District Cost of Funds Interest Determination Date”), the rate equal to the monthly weighted average cost of funds for the calendar month immediately preceding the month in which the Eleventh District Cost of Funds Interest Determination Date falls as set forth under the caption “11th District” on the display on Reuters (or any successor service) on page COFI/ARMS (or any other page as may replace the specified page on that service) (“COFI/ARMS Page”), or if not so displayed, on Bloomberg service (or any successor service) on page ALLX COF (or any other page as may replace the specified page on that service) (“Bloomberg page ALLX COF”) in each case, as of 11:00 A.M., San Francisco time, on the Eleventh District Cost of Funds Interest Determination Date. If such rate does not appear on the COFI/ARMS Page or Bloomberg Page ALLX COF on any related Eleventh District Cost of Funds Interest Determination Date, the Eleventh District Cost of Funds Rate for the Eleventh District Cost of Funds Interest Determination Date will be the Eleventh District Cost of Funds Rate Index, as defined below. If the FHLB of San Francisco fails to announce the rate for the calendar month next preceding the Eleventh District Cost of Funds Interest Determination Date, then the Eleventh District Cost of Funds Rate for that date will be the Eleventh District Cost of Funds Rate in effect on that Eleventh District Cost of Funds Interest Determination Date."
> For the US, tzdb actually provides less ability to solve this problem.
> Even if tzdb had an ID for each State, that would be insufficient to
> cleanly map a location to a good enough ID. In the US, tzdb
> effectively doesn't help a user find itz info for Piscataway, NJ -
> something must *directly* connect Piscataway with America/New_York -
> no other geographic hierarchy such as the State will do.
> ie. in Europe, you can map location to country (typically easy to do)
> and then country to timezone ID (easy) and be happy with the outcome.
> In the US, you would need a direct mapping from location to timezone
> for thousands of locations because there is no suitable intermediate
> location hierarchy. An abstract region model is the only one that
> really works for the US.
What's the difference between "map location to country" and "map location to tzdb ID" that renders the former "easy to do" in Europe but that renders the latter *not* easy to do in Europe? Is it that the former doesn't need direct mapping from location to country, so that even with a larger number of cities in Europe, you wouldn't need a table that gives the country for all of those cities?
> Why does this matter in this discussion? Well, one thing I don't want
> to see in tzdb is an attempt to force the US model onto Europe. The
> extra level of country implicit in the European zone IDs is really
> useful to applications.
1) you're expressing concern for applications that *only* have to deal with times in "Europe" in the sense of "that region on the Eurasian continent where countries don't have more than one tzdb region"
2) you're expressing concern for application that use *different* algorithms for selecting tzdb IDs to represent "XXX Time", where the algorithm used to map between "XXX Time" and a tzdb region is "map XXX time to a country and then map that country to a tzdb region", and don't want those applications to have to come up with a different algorithm for Europe.
> And part of this discussion is to tease out the implicit and make it explicit.
Which is exactly what I've been doing in the past couple of messages.
So, let's make it explicit in which regions of the world it's important that "map "XXX Time" to a country and map a country to a tzdb region" must work, with the rest of the world possibly using "map "XXX time" directly to a tzdb region" (an algorithm that would *also* work for Europe).
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