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Diffstat (limited to 'usr.sbin/zic/Theory')
| -rw-r--r-- | usr.sbin/zic/Theory | 313 |
1 files changed, 290 insertions, 23 deletions
diff --git a/usr.sbin/zic/Theory b/usr.sbin/zic/Theory index 1c43133..cbf53b9 100644 --- a/usr.sbin/zic/Theory +++ b/usr.sbin/zic/Theory @@ -1,4 +1,4 @@ -@(#)Theory 7.6 +@(#)Theory 7.15 ----- Outline ----- @@ -6,12 +6,14 @@ Time and date functions Names of time zone regions Time zone abbreviations + Calendrical issues + Time and time zones on Mars ----- Time and date functions ----- These time and date functions are upwards compatible with POSIX.1, -an international standard for Unix-like systems. +an international standard for UNIX-like systems. As of this writing, the current edition of POSIX.1 is: Information technology --Portable Operating System Interface (POSIX (R)) @@ -34,7 +36,7 @@ POSIX.1 has the following properties and limitations. stdoffset[dst[offset],date[/time],date[/time]] where: - + std and dst are 3 or more characters specifying the standard and daylight saving time (DST) zone names. @@ -143,7 +145,7 @@ Points of interest to folks with other systems: since the format of zic's input changed slightly in late 1994, and many vendors still do not support the new input format. -* The Unix Version 7 "timezone" function is not present in this package; +* The UNIX Version 7 "timezone" function is not present in this package; it's impossible to reliably map timezone's arguments (a "minutes west of GMT" value and a "daylight saving time in effect" flag) to a time zone abbreviation, and we refuse to guess. @@ -178,11 +180,34 @@ so much the better. ----- Names of time zone rule files ----- -The names of this package's installed time zone rule files are chosen to -help minimize possible future incompatibilities due to political events. -Ordinarily, names of countries are not used, to avoid incompatibilities -when countries change their name (e.g. Zaire->Congo) or -when locations change countries (e.g. Hong Kong from UK colony to China). +The time zone rule file naming conventions attempt to strike a balance +among the following goals: + + * Uniquely identify every national region where clocks have all + agreed since 1970. This is essential for the intended use: static + clocks keeping local civil time. + + * Indicate to humans as to where that region is. This simplifes use. + + * Be robust in the presence of political changes. This reduces the + number of updates and backward-compatibility hacks. For example, + names of countries are ordinarily not used, to avoid + incompatibilities when countries change their name + (e.g. Zaire->Congo) or when locations change countries + (e.g. Hong Kong from UK colony to China). + + * Be portable to a wide variety of implementations. + This promotes use of the technology. + + * Use a consistent naming convention over the entire world. + This simplifies both use and maintenance. + +This naming convention is not intended for use by inexperienced users +to select TZ values by themselves (though they can of course examine +and reuse existing settings). Distributors should provide +documentation and/or a simple selection interface that explains the +names; see the 'tzselect' program supplied with this distribution for +one example. Names normally have the form AREA/LOCATION, where AREA is the name of a continent or ocean, and LOCATION is the name of a specific @@ -193,11 +218,16 @@ and `Pacific/Honolulu'. Here are the general rules used for choosing location names, in decreasing order of importance: - Use only valid Posix file names. Use only Ascii letters, digits, `.', - `-' and `_'. Do not exceed 14 characters or start with `-'. - E.g. prefer `Brunei' to `Bandar_Seri_Begawan'. + Use only valid POSIX file name components (i.e., the parts of + names other than `/'). Within a file name component, + use only ASCII letters, `.', `-' and `_'. Do not use + digits, as that might create an ambiguity with POSIX + TZ strings. A file name component must not exceed 14 + characters or start with `-'. E.g., prefer `Brunei' + to `Bandar_Seri_Begawan'. Include at least one location per time zone rule set per country. - One such location is enough. + One such location is enough. Use ISO 3166 (see the file + iso3166.tab) to help decide whether something is a country. If all the clocks in a country's region have agreed since 1970, don't bother to include more than one location even if subregions' clocks disagreed before 1970. @@ -209,9 +239,9 @@ in decreasing order of importance: or regions, so that any future time zone changes do not split locations into different time zones. E.g. prefer `Paris' to `France', since France has had multiple time zones. - Use traditional English spelling, e.g. prefer `Rome' to `Roma', and + Use mainstream English spelling, e.g. prefer `Rome' to `Roma', and prefer `Athens' to the true name (which uses Greek letters). - The Posix file name restrictions encourage this rule. + The POSIX file name restrictions encourage this rule. Use the most populous among locations in a country's time zone, e.g. prefer `Shanghai' to `Beijing'. Among locations with similar populations, pick the best-known location, @@ -225,13 +255,19 @@ in decreasing order of importance: Use `_' to represent a space. Omit `.' from abbreviations in names, e.g. prefer `St_Helena' to `St._Helena'. + Do not change established names if they only marginally + violate the above rules. For example, don't change + the existing name `Rome' to `Milan' merely because + Milan's population has grown to be somewhat greater + than Rome's. + If a name is changed, put its old spelling in the `backward' file. The file `zone.tab' lists the geographical locations used to name time zone rule files. Older versions of this package used a different naming scheme, and these older names are still supported. -See the file `backwards' for most of these older names +See the file `backward' for most of these older names (e.g. `US/Eastern' instead of `America/New_York'). The other old-fashioned names still supported are `WET', `CET', `MET', `EET' (see the file `europe'), @@ -245,25 +281,39 @@ like `EST' to be compatible with human tradition and POSIX.1. Here are the general rules used for choosing time zone abbreviations, in decreasing order of importance: - Use abbreviations that consist of 3 or more upper-case Ascii letters, - except use "___" for locations while uninhabited. - Posix.1 requires at least 3 characters, and the restriction to - upper-case Ascii letters follows most traditions. + Use abbreviations that consist of three or more ASCII letters. Previous editions of this database also used characters like ' ' and '?', but these characters have a special meaning to the shell and cause commands like set `date` - to have unexpected effects. In theory, the character set could - be !%./@A-Z^_a-z{}, but these tables use only upper-case - Ascii letters (and "___"). + to have unexpected effects. + Previous editions of this rule required upper-case letters, + but the Congressman who introduced Chamorro Standard Time + preferred "ChST", so the rule has been relaxed. + + This rule guarantees that all abbreviations could have + been specified by a POSIX.1 TZ string. POSIX.1 + requires at least three characters for an + abbreviation. POSIX.1-1996 says that an abbreviation + cannot start with ':', and cannot contain ',', '-', + '+', NUL, or a digit. Draft 7 of POSIX 1003.1-200x + changes this rule to say that an abbreviation can + contain only '-', '+', and alphanumeric characters in + the current locale. To be portable to both sets of + rules, an abbreviation must therefore use only ASCII + letters, as these are the only letters that are + alphabetic in all locales. + Use abbreviations that are in common use among English-speakers, e.g. `EST' for Eastern Standard Time in North America. We assume that applications translate them to other languages as part of the normal localization process; for example, a French application might translate `EST' to `HNE'. + For zones whose times are taken from a city's longitude, use the traditional xMT notation, e.g. `PMT' for Paris Mean Time. The only name like this in current use is `GMT'. + If there is no common English abbreviation, abbreviate the English translation of the usual phrase used by native speakers. If this is not available or is a phrase mentioning the country @@ -278,8 +328,225 @@ in decreasing order of importance: and then append `T', `ST', etc. as before; e.g. `VLAST' for VLAdivostok Summer Time. + Use "zzz" for locations while uninhabited. The mnemonic is that + these locations are, in some sense, asleep. + Application writers should note that these abbreviations are ambiguous in practice: e.g. `EST' has a different meaning in Australia than it does in the United States. In new applications, it's often better to use numeric UTC offsets like `-0500' instead of time zone abbreviations like `EST'; this avoids the ambiguity. + + +----- Calendrical issues ----- + +Calendrical issues are a bit out of scope for a time zone database, +but they indicate the sort of problems that we would run into if we +extended the time zone database further into the past. An excellent +resource in this area is Nachum Dershowitz and Edward M. Reingold, +<a href="http://emr.cs.uiuc.edu/home/reingold/calendar-book/index.shtml"> +Calendrical Calculations +</a>, Cambridge University Press (1997). Other information and +sources are given below. They sometimes disagree. + + +France + +Gregorian calendar adopted 1582-12-20. +French Revolutionary calendar used 1793-11-24 through 1805-12-31, +and (in Paris only) 1871-05-06 through 1871-05-23. + + +Russia + +From Chris Carrier <72157.3334@CompuServe.COM> (1996-12-02): +On 1929-10-01 the Soviet Union instituted an ``Eternal Calendar'' +with 30-day months plus 5 holidays, with a 5-day week. +On 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the +Gregorian calendar while retaining the 6-day week; on 1940-06-27 it +reverted to the 7-day week. With the 6-day week the usual days +off were the 6th, 12th, 18th, 24th and 30th of the month. +(Source: Evitiar Zerubavel, _The Seven Day Circle_) + + +Mark Brader reported a similar story in "The Book of Calendars", edited +by Frank Parise (1982, Facts on File, ISBN 0-8719-6467-8), page 377. But: + +From: Petteri Sulonen (via Usenet) +Date: 14 Jan 1999 00:00:00 GMT +Message-ID: <Petteri.Sulonen-1401991626030001@lapin-kulta.in.helsinki.fi> + +If your source is correct, how come documents between 1929 -- 1940 were +still dated using the conventional, Gregorian calendar? + +I can post a scan of a document dated December 1, 1934, signed by +Yenukidze, the secretary, on behalf of Kalinin, the President of the +Executive Committee of the Supreme Soviet, if you like. + + + +Sweden (and Finland) + +From: msb@sq.com (Mark Brader) +<a href="news:1996Jul6.012937.29190@sq.com"> +Subject: Re: Gregorian reform -- a part of locale? +</a> +Date: 1996-07-06 + +In 1700, Denmark made the transition from Julian to Gregorian. Sweden +decided to *start* a transition in 1700 as well, but rather than have one of +those unsightly calendar gaps :-), they simply decreed that the next leap +year after 1696 would be in 1744 -- putting the whole country on a calendar +different from both Julian and Gregorian for a period of 40 years. + +However, in 1704 something went wrong and the plan was not carried through; +they did, after all, have a leap year that year. And one in 1708. In 1712 +they gave it up and went back to Julian, putting 30 days in February that +year!... + +Then in 1753, Sweden made the transition to Gregorian in the usual manner, +getting there only 13 years behind the original schedule. + +(A previous posting of this story was challenged, and Swedish readers +produced the following references to support it: "Tiderakning och historia" +by Natanael Beckman (1924) and "Tid, en bok om tiderakning och +kalendervasen" by Lars-Olof Lode'n (no date was given).) + + +Grotefend's data + +From: "Michael Palmer" <mpalmer@netcom.com> [with one obvious typo fixed] +Subject: Re: Gregorian Calendar (was Re: Another FHC related question +Newsgroups: soc.genealogy.german +Date: Tue, 9 Feb 1999 02:32:48 -800 +Message-ID: <199902091032.CAA09644@netcom10.netcom.com> + +The following is a(n incomplete) listing, arranged chronologically, of +European states, with the date they converted from the Julian to the +Gregorian calendar: + +04/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman + Catholics and Danzig only) +09/20 Dec 1582 - France, Lorraine + +21 Dec 1582/ + 01 Jan 1583 - Holland, Brabant, Flanders, Hennegau +10/21 Feb 1583 - bishopric of Liege (L"uttich) +13/24 Feb 1583 - bishopric of Augsburg +04/15 Oct 1583 - electorate of Trier +05/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg, + Salzburg, Brixen +13/24 Oct 1583 - Austrian Oberelsass and Breisgau +20/31 Oct 1583 - bishopric of Basel +02/13 Nov 1583 - duchy of J"ulich-Berg +02/13 Nov 1583 - electorate and city of K"oln +04/15 Nov 1583 - bishopric of W"urzburg +11/22 Nov 1583 - electorate of Mainz +16/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden +17/28 Nov 1583 - bishopric of M"unster and duchy of Cleve +14/25 Dec 1583 - Steiermark + +06/17 Jan 1584 - Austria and Bohemia +11/22 Jan 1584 - Luzern, Uri, Schwyz, Zug, Freiburg, Solothurn +12/23 Jan 1584 - Silesia and the Lausitz +22 Jan/ + 02 Feb 1584 - Hungary (legally on 21 Oct 1587) + Jun 1584 - Unterwalden +01/12 Jul 1584 - duchy of Westfalen + +16/27 Jun 1585 - bishopric of Paderborn + +14/25 Dec 1590 - Transylvania + +22 Aug/ + 02 Sep 1612 - duchy of Prussia + +13/24 Dec 1614 - Pfalz-Neuburg + + 1617 - duchy of Kurland (reverted to the Julian calendar in + 1796) + + 1624 - bishopric of Osnabr"uck + + 1630 - bishopric of Minden + +15/26 Mar 1631 - bishopric of Hildesheim + + 1655 - Kanton Wallis + +05/16 Feb 1682 - city of Strassburg + +18 Feb/ + 01 Mar 1700 - Protestant Germany (including Swedish possessions in + Germany), Denmark, Norway +30 Jun/ + 12 Jul 1700 - Gelderland, Zutphen +10 Nov/ + 12 Dec 1700 - Utrecht, Overijssel + +31 Dec 1700/ + 12 Jan 1701 - Friesland, Groningen, Z"urich, Bern, Basel, Geneva, + Turgau, and Schaffhausen + + 1724 - Glarus, Appenzell, and the city of St. Gallen + +01 Jan 1750 - Pisa and Florence + +02/14 Sep 1752 - Great Britain + +17 Feb/ + 01 Mar 1753 - Sweden + +1760-1812 - Graub"unden + +The Russian empire (including Finland and the Baltic states) did not +convert to the Gregorian calendar until the Soviet revolution of 1917. + +Source: H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen +Mittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend +(Hannover: Hahnsche Buchhandlung, 1941), pp. 26-28. + + +----- Time and time zones on Mars ----- + +Some people have adjusted their work schedules to fit Mars time. +Dozens of special Mars watches were built for Jet Propulsion +Laboratory workers who kept Mars time during the Mars Exploration +Rovers mission (2004). These timepieces look like normal Seikos and +Citizens but use Mars seconds rather than terrestrial seconds. + +A Mars solar day is called a "sol" and has a mean period equal to +about 24 hours 39 minutes 35.244 seconds in terrestrial time. It is +divided into a conventional 24-hour clock, so each Mars second equals +about 1.02749125 terrestrial seconds. + +The prime meridian of Mars goes through the center of the crater +Airy-0, named in honor of the British astronomer who built the +Greenwich telescope that defines Earth's prime meridian. Mean solar +time on the Mars prime meridian is called Mars Coordinated Time (MTC). + +Each landed mission on Mars has adopted a different reference for +solar time keeping, so there is no real standard for Mars time zones. +For example, the Mars Exploration Rover project (2004) defined two +time zones "Local Solar Time A" and "Local Solar Time B" for its two +missions, each zone designed so that its time equals local true solar +time at approximately the middle of the nominal mission. Such a "time +zone" is not particularly suited for any application other than the +mission itself. + +Many calendars have been proposed for Mars, but none have achieved +wide acceptance. Astronomers often use Mars Sol Date (MSD) which is a +sequential count of Mars solar days elapsed since about 1873-12-29 +12:00 GMT. + +The tz database does not currently support Mars time, but it is +documented here in the hopes that support will be added eventually. + +Sources: + +Michael Allison and Robert Schmunk, +"Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock" +<http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2004-03-15). + +Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times +(2004-01-14), pp A1, A20-A21. |
