Since sending this message, Alois has joined the time zone mailing list. --ado -----Original Message----- From: Alois Treindl [mailto:alois@astro.ch] Sent: Thursday, March 10, 2005 5:54 AM To: Olson, Arthur David (NIH/NCI) Cc: Tz (tz@elsie.nci.nih.gov) Subject: Re: Time zone: the next generation On Thu, 3 Mar 2005, Olson, Arthur David (NIH/NCI) wrote:

QUESTIONS

* Do we handle Julian/Gregorian transitions?

Yes, but with an override feature in the API. One of the problems is that many history texts contain converted calendar dates. For the consistency of a particular history book, biography etc, authors have a tendency to convert all calendar data contained in them into one system, even if at the given date and location a different calendar might have applied. If a related calendar/timezone database makes strict assumptions about which calendar applied for a given date, then new problems are introduced.

* Do we allow control of skipping the year zero?

Both styles of year counting have a name. The one with year zero is called 'astronomical year counting style' and it indicates years BC with negative year numbers. The one without year zero is called 'historical year counting style' and it indicates years BC with the suffix BC or BCE or something similar, but never with a plus/minus sign. I think the documentation should be clear, but the API needs only to support one style.

* Do we handle pegging of far-past and far-future times?

Aside from calendar system changes, no time zone data are known for dates before the 1800s. There is an issue whether true solar time or mean solar time was used for the recording of a particular historical event. But I do not see how tzdata should be able to answer this question. E.g. when J.W.Goethe mentions in one of his works that he was born at noon on 28 August 1749 (greg. calendar) in Frankfurt: Does he mean true solar time (as indicated by a sun dial) or mean solar time (as measured by an astronomical clock in an observatory)? tzdata cannot know this, and should not claim that it knows. There was no clear transition between true solar time and mean solar time reckoning, before the formal introduction of timezone standards in the 19th century. Alois Treindl