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Subject: RE: [office] ODF 1.2 draft 7 - table chapter

"Authority" means several different things.  It might be the civil or 
religious authority that mandates the use of a calendar.  Or it may be the 
first author to fully describe the calendar.  Or it may be a modern 
reference that fully describes the existing practice.

For Gregorian calendar, the original authority was, as you might imagine, 
Pope Gregory's bull "Inter gravisimas".  But that is not the legal 
authority, at least not in the US.  The authority for the US (or at that 
time the British Colonies) was the Act 24 Geo. 2. c. 23 which said:

"Be it further enacted by the Authority aforesaid, that the several Years 
of our Lord, 1800, 1900, 2100, 2200, 2300, or any other hundredth Years of 
our Lord, which shall happen in Time to come, except only every fourth 
hundredth Year of our Lord, whereof the Year of our Lord 2000 shall be the 
first, shall not be esteemed or taken to be Bissextile or Leap Years, but 
shall be taken to be common Years, consisting of 365 Days, and no more."

Of course, the path to the Gregorian calendar probably took a less direct 
route in former French or Spanish territories that now are part if the 
U.S.  When you combine that with the near (but not exactly) 
contemporaneous adoption of January 1st as the beginning of the New Year, 
and it is difficult to nail an authority.  Conventionally we just say 
apply Gregorian after 1582 and pretend that it happened all over the world 
at the same time, which it didn't.  So doing internationally date math in 
the period 1582-1752 is treacherous.

I could see burning a lot of digital ink on trying to solve this problem. 
But we might consider when this is something akin to trying to define 
"bold" in text, or defining what the "red" value in an RGB triplet means, 
or defining a language code.  We're allowed to specify a language code of 
"de_ch", but we are not obliged to define and explain what exactly 
comprises the Swiss Germany dialect.


"Dennis E. Hamilton" <dennis.hamilton@acm.org> wrote on 10/30/2008 
08:42:17 PM:
> I am a calendar and date-time algorithm junky, so this exchange provoked 
> little research on my part.
> I don't have any insight about the non-Gregorian calendars, but it would 
> great to provided references to authoritative sources that can be 
> and used.
> For the Gregorian calendar,
> It strikes me that IS 29500 punts on the rules for Gregorian Calendars 
> much as ODF does, although ISO 8601 does specify the Gregorian calendar 
> an indirect way.  If you know the rule for leap years plus the standard
> calendar, all you need to do to make a Gregorian Calendar is know the 
day of
> the week of January 1 for that year.  (It is a Saturday for every 
> year whose number is a multiple of 400.)  There is sufficient 
information to
> deduce reliable rules from that much.  ISO 8601 is more about recording 
> dates than computing them. ISO 8601 is rather vague around specification 
> durations without known context when there are units larger than days.
> There are two old (ISO 30 and ISO 31) specifications that are referenced 
> the fundamentals and maybe they help with regard to time sequences.
> I have no idea where one might find a better, authoritative modern 
source on
> the Gregorian Calendar.  Someone must have something (although the
> experience with time intervals in financial calculations gives me doubt
> where I previously had none).  My sparse collection of ISO standards 
> far back to ISO 2014 (writing calendar dates in numeric form), ISO 3307
> (representations of time of day) and ISO 4031 (representation of local 
> differentials), etc.  None of these have to deal with the fine details 
> date-time comparisons, calculations, day-of-week determination, etc., 
> 8601 supplants them anyhow.  Methods are neither specified nor 
referenced in
> ISO 8601.
> Oddly, the treatment in Wikipedia is valuable (and the External links 
> out to a downloadable copy of ISO 8601:2004):
> http://en.wikipedia.org/wiki/ISO_8601
> The treatment of the Gregorian Calendar is also intriguing: 
> http://en.wikipedia.org/wiki/Gregorian_calendar 
> Every Gregorian year number divisible by 400 has the same calendar and
> January 1 is a Saturday.  Also, there is a 400-year cycle (natch) but 
> are actually only 14 different calendars for Gregorian years and you can
> pick the right one using anything equivalent to the Doomsday algorithm:
> Figure out what the day of the week for January 1 is and also determine
> whether February has 28 or 29 days. There are many little arithmetic
> shortcuts that can be used. 
>  - Dennis
> PS: What we probably don't care about so much, but should probably be
> accounted for in an authoritative source, is the difference between what 
> Gregorian date would have been for a relatively-remote past/future day 
> so-called proleptic Gregorian calendar in the case of past dates in 
> before the Gregorian calendar was in use) and the date according to the
> calendar system that was/will-be actually in use.  (If we are talking 
> dates as recorded at the time, we must be careful to avoid confusing 
> with what the extrapolated Gregorian Calendar date turns out to be,
> however.) There are, of course, non-Gregorian calendars in use to this 
> and converting among them is important.
> PPS: If we consider *time*, not just date, there are also those pesky
> time-adjustment events that happen from time to time.  I suspect that we
> don't care about those, but astrophysics scientist might have some
> information on the matter.  Perhaps on the matter of time there is more
> interest in the noise around time zones and various local-time 
> (e.g., summer time and daylight savings times) in understanding the 
> and synchronicity of events in time.  Also an interesting challenge, but
> maybe not a high priority among those where we may need more precision 
> specification.  ISO 8601 indicates how to record everything that comes 
up in
> these contexts, but it doesn't say how to find them.
> -----Original Message-----
> From: Patrick Durusau [mailto:patrick@durusau.net] 
> http://lists.oasis-open.org/archives/office/200810/msg00168.html 
> Sent: Thursday, October 30, 2008 10:52
> To: office@lists.oasis-open.org
> Subject: Re: [office] ODF 1.2 draft 7 - table chapter
> Eike,
> Just quickly but looking at ST_CalendarType (Calendar Types) in ISO/IEC 
> 29500 I see:
> gregorian (Gregorian) Specifies that the Gregorian calendar, as defined 
> in ISO
> 8601, shall be used. This calendar should be localized
> into the appropriate language.
> [ ... ]
> hebrew (Hebrew) Specifies that the Hebrew lunar calendar, as described
> by the Gauss formula for Passover [CITATION] and The
> Complete Restatement of Oral Law (Mishneh Torah),
> shall be used.
> hijri (Hijri) Specifies that the Hijri lunar calendar, as described by
> the Kingdom of Saudi Arabia, Ministry of Islamic
> Affairs, Endowments, Da?wah and Guidance, shall be
> used.
> japan (Japanese Emperor Era) Specifies that the Japanese Emperor Era 
> calendar, as
> described by Japanese Industrial Standard JIS X 0301,
> shall be used.
> korea (Korean Tangun Era) Specifies that the Korean Tangun Era calendar, 
> described by Korean Law Enactment No. 4, shall be
> used.
> none (No Calendar Type) Specifies that no calendar should be used.
> saka (Saka Era) Specifies that the Saka Era calendar, as described by
> the Calendar Reform Committee of India, as part of
> the Indian Ephemeris and Nautical Almanac, shall be
> used.
> taiwan (Taiwan) Specifies that the Taiwanese calendar, as defined by
> the Chinese National Standard CNS 7648, shall be
> used.
> thai (Thai) Specifies that the Thai calendar, as defined by the
> Royal Decree of H.M. King Vajiravudh (Rama VI) in
> Royal Gazette B. E. 2456 (1913 A.D.) and by the decree
> of Prime Minister Phibunsongkhram (1941 A.D.) to
> start the year on the Gregorian January 1 and to map
> year zero to Gregorian year 543 B.C., shall be used.
> [ ... ]
> PS: Which raises the interesting issue of what we should do if we find 
> one or more of these definitions sufficient? Should we simply cite the 
> existing definition? Or for that matter, do we really need to re-define 
> Add? Seems like one definition may be enough. Assuming they are 
> semantically equivalent. May not be so I am not making a claim that they 

> are. But I do think we need to look to see.
> Eike Rathke wrote:
> http://lists.oasis-open.org/archives/office/200810/msg00166.html
> [ ... ]
> >
> > Btw, regarding definitions of various calendars it seems to be hard to
> > find normative references for any of them. You mentioned that ISO has
> > a standard about the Gregorian calendar, I found only ISO 8601 that
> > seems to specify that it is the calendar as specified by Pope Gregory
> > XIII in 1582, and a few dates as reference points such as the metric
> > convention being signed on 1875-05-20 and 2000-01-01 being Saturday 
> > defined. Is that what you were referring, or is there something else?
> > I don't have a copy of the full standard at hand.
> >
> >   Eike
> [ ... ]
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