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Subject: RE: [office] ODF 1.2 draft 7 - table chapter
I am a calendar and date-time algorithm junky, so this exchange provoked a little research on my part. I don't have any insight about the non-Gregorian calendars, but it would be great to provided references to authoritative sources that can be located and used. For the Gregorian calendar, It strikes me that IS 29500 punts on the rules for Gregorian Calendars as much as ODF does, although ISO 8601 does specify the Gregorian calendar in 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 Gregorian 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 the dates than computing them. ISO 8601 is rather vague around specification of durations without known context when there are units larger than days. There are two old (ISO 30 and ISO 31) specifications that are referenced for 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 refers far back to ISO 2014 (writing calendar dates in numeric form), ISO 3307 (representations of time of day) and ISO 4031 (representation of local time differentials), etc. None of these have to deal with the fine details of date-time comparisons, calculations, day-of-week determination, etc., and 8601 supplants them anyhow. Methods are neither specified nor referenced in ISO 8601. Oddly, the treatment in Wikipedia is valuable (and the External links reach 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 there 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 the Gregorian date would have been for a relatively-remote past/future day (the so-called proleptic Gregorian calendar in the case of past dates in places 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 about dates as recorded at the time, we must be careful to avoid confusing them with what the extrapolated Gregorian Calendar date turns out to be, however.) There are, of course, non-Gregorian calendars in use to this day, 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 adjustments (e.g., summer time and daylight savings times) in understanding the sequence and synchronicity of events in time. Also an interesting challenge, but maybe not a high priority among those where we may need more precision of 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, as 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 are > 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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