Theory revision 1.10
1# $NetBSD: Theory,v 1.10 2011/09/04 10:10:26 christos Exp $ 2@(#)Theory 8.6 3This file is in the public domain, so clarified as of 42009-05-17 by Arthur David Olson. 5 6----- Outline ----- 7 8 Time and date functions 9 Scope of the tz database 10 Names of time zone rule files 11 Time zone abbreviations 12 Calendrical issues 13 Time and time zones on Mars 14 15----- Time and date functions ----- 16 17These time and date functions are upwards compatible with POSIX, 18an international standard for UNIX-like systems. 19As of this writing, the current edition of POSIX is: 20 21 Standard for Information technology 22 -- Portable Operating System Interface (POSIX (R)) 23 -- System Interfaces 24 IEEE Std 1003.1, 2004 Edition 25 <http://www.opengroup.org/online-pubs?DOC=7999959899> 26 <http://www.opengroup.org/pubs/catalog/t041.htm> 27 28POSIX has the following properties and limitations. 29 30* In POSIX, time display in a process is controlled by the 31 environment variable TZ. Unfortunately, the POSIX TZ string takes 32 a form that is hard to describe and is error-prone in practice. 33 Also, POSIX TZ strings can't deal with other (for example, Israeli) 34 daylight saving time rules, or situations where more than two 35 time zone abbreviations are used in an area. 36 37 The POSIX TZ string takes the following form: 38 39 stdoffset[dst[offset],date[/time],date[/time]] 40 41 where: 42 43 std and dst 44 are 3 or more characters specifying the standard 45 and daylight saving time (DST) zone names. 46 Starting with POSIX.1-2001, std and dst may also be 47 in a quoted form like "<UTC+10>"; this allows 48 "+" and "-" in the names. 49 offset 50 is of the form `[-]hh:[mm[:ss]]' and specifies the 51 offset west of UTC. The default DST offset is one hour 52 ahead of standard time. 53 date[/time],date[/time] 54 specifies the beginning and end of DST. If this is absent, 55 the system supplies its own rules for DST, and these can 56 differ from year to year; typically US DST rules are used. 57 time 58 takes the form `hh:[mm[:ss]]' and defaults to 02:00. 59 date 60 takes one of the following forms: 61 Jn (1<=n<=365) 62 origin-1 day number not counting February 29 63 n (0<=n<=365) 64 origin-0 day number counting February 29 if present 65 Mm.n.d (0[Sunday]<=d<=6[Saturday], 1<=n<=5, 1<=m<=12) 66 for the dth day of week n of month m of the year, 67 where week 1 is the first week in which day d appears, 68 and `5' stands for the last week in which day d appears 69 (which may be either the 4th or 5th week). 70 71 Here is an example POSIX TZ string, for US Pacific time using rules 72 appropriate from 1987 through 2006: 73 74 TZ='PST8PDT,M4.1.0/02:00,M10.5.0/02:00' 75 76 This POSIX TZ string is hard to remember, and mishandles time stamps 77 before 1987 and after 2006. With this package you can use this 78 instead: 79 80 TZ='America/Los_Angeles' 81 82* POSIX does not define the exact meaning of TZ values like "EST5EDT". 83 Typically the current US DST rules are used to interpret such values, 84 but this means that the US DST rules are compiled into each program 85 that does time conversion. This means that when US time conversion 86 rules change (as in the United States in 1987), all programs that 87 do time conversion must be recompiled to ensure proper results. 88 89* In POSIX, there's no tamper-proof way for a process to learn the 90 system's best idea of local wall clock. (This is important for 91 applications that an administrator wants used only at certain times-- 92 without regard to whether the user has fiddled the "TZ" environment 93 variable. While an administrator can "do everything in UTC" to get 94 around the problem, doing so is inconvenient and precludes handling 95 daylight saving time shifts--as might be required to limit phone 96 calls to off-peak hours.) 97 98* POSIX requires that systems ignore leap seconds. 99 100These are the extensions that have been made to the POSIX functions: 101 102* The "TZ" environment variable is used in generating the name of a file 103 from which time zone information is read (or is interpreted a la 104 POSIX); "TZ" is no longer constrained to be a three-letter time zone 105 name followed by a number of hours and an optional three-letter 106 daylight time zone name. The daylight saving time rules to be used 107 for a particular time zone are encoded in the time zone file; 108 the format of the file allows U.S., Australian, and other rules to be 109 encoded, and allows for situations where more than two time zone 110 abbreviations are used. 111 112 It was recognized that allowing the "TZ" environment variable to 113 take on values such as "America/New_York" might cause "old" programs 114 (that expect "TZ" to have a certain form) to operate incorrectly; 115 consideration was given to using some other environment variable 116 (for example, "TIMEZONE") to hold the string used to generate the 117 time zone information file name. In the end, however, it was decided 118 to continue using "TZ": it is widely used for time zone purposes; 119 separately maintaining both "TZ" and "TIMEZONE" seemed a nuisance; 120 and systems where "new" forms of "TZ" might cause problems can simply 121 use TZ values such as "EST5EDT" which can be used both by 122 "new" programs (a la POSIX) and "old" programs (as zone names and 123 offsets). 124 125* To handle places where more than two time zone abbreviations are used, 126 the functions "localtime" and "gmtime" set tzname[tmp->tm_isdst] 127 (where "tmp" is the value the function returns) to the time zone 128 abbreviation to be used. This differs from POSIX, where the elements 129 of tzname are only changed as a result of calls to tzset. 130 131* Since the "TZ" environment variable can now be used to control time 132 conversion, the "daylight" and "timezone" variables are no longer 133 needed. (These variables are defined and set by "tzset"; however, their 134 values will not be used by "localtime.") 135 136* The "localtime" function has been set up to deliver correct results 137 for near-minimum or near-maximum time_t values. (A comment in the 138 source code tells how to get compatibly wrong results). 139 140* A function "tzsetwall" has been added to arrange for the system's 141 best approximation to local wall clock time to be delivered by 142 subsequent calls to "localtime." Source code for portable 143 applications that "must" run on local wall clock time should call 144 "tzsetwall();" if such code is moved to "old" systems that don't 145 provide tzsetwall, you won't be able to generate an executable program. 146 (These time zone functions also arrange for local wall clock time to be 147 used if tzset is called--directly or indirectly--and there's no "TZ" 148 environment variable; portable applications should not, however, rely 149 on this behavior since it's not the way SVR2 systems behave.) 150 151* These functions can account for leap seconds, thanks to Bradley White. 152 153Points of interest to folks with other systems: 154 155* This package is already part of many POSIX-compliant hosts, 156 including BSD, HP, Linux, Network Appliance, SCO, SGI, and Sun. 157 On such hosts, the primary use of this package 158 is to update obsolete time zone rule tables. 159 To do this, you may need to compile the time zone compiler 160 `zic' supplied with this package instead of using the system `zic', 161 since the format of zic's input changed slightly in late 1994, 162 and many vendors still do not support the new input format. 163 164* The UNIX Version 7 "timezone" function is not present in this package; 165 it's impossible to reliably map timezone's arguments (a "minutes west 166 of GMT" value and a "daylight saving time in effect" flag) to a 167 time zone abbreviation, and we refuse to guess. 168 Programs that in the past used the timezone function may now examine 169 tzname[localtime(&clock)->tm_isdst] to learn the correct time 170 zone abbreviation to use. Alternatively, use 171 localtime(&clock)->tm_zone if this has been enabled. 172 173* The 4.2BSD gettimeofday function is not used in this package. 174 This formerly let users obtain the current UTC offset and DST flag, 175 but this functionality was removed in later versions of BSD. 176 177* In SVR2, time conversion fails for near-minimum or near-maximum 178 time_t values when doing conversions for places that don't use UTC. 179 This package takes care to do these conversions correctly. 180 181The functions that are conditionally compiled if STD_INSPIRED is defined 182should, at this point, be looked on primarily as food for thought. They are 183not in any sense "standard compatible"--some are not, in fact, specified in 184*any* standard. They do, however, represent responses of various authors to 185standardization proposals. 186 187Other time conversion proposals, in particular the one developed by folks at 188Hewlett Packard, offer a wider selection of functions that provide capabilities 189beyond those provided here. The absence of such functions from this package 190is not meant to discourage the development, standardization, or use of such 191functions. Rather, their absence reflects the decision to make this package 192contain valid extensions to POSIX, to ensure its broad acceptability. If 193more powerful time conversion functions can be standardized, so much the 194better. 195 196 197----- Scope of the tz database ----- 198 199The tz database attempts to record the history and predicted future of 200all computer-based clocks that track civil time. To represent this 201data, the world is partitioned into regions whose clocks all agree 202about time stamps that occur after the somewhat-arbitrary cutoff point 203of the POSIX Epoch (1970-01-01 00:00:00 UTC). For each such region, 204the database records all known clock transitions, and labels the region 205with a notable location. 206 207Clock transitions before 1970 are recorded for each such location, 208because most POSIX-compatible systems support negative time stamps and 209could misbehave if data were omitted for pre-1970 transitions. 210However, the database is not designed for and does not suffice for 211applications requiring accurate handling of all past times everywhere, 212as it would take far too much effort and guesswork to record all 213details of pre-1970 civil timekeeping. 214 215As noted in the README file, the tz database is not authoritative 216(particularly not for pre-1970 time stamps), and it surely has errors. 217Corrections are welcome and encouraged. Users requiring authoritative 218data should consult national standards bodies and the references cited 219in the database's comments. 220 221 222----- Names of time zone rule files ----- 223 224The time zone rule file naming conventions attempt to strike a balance 225among the following goals: 226 227 * Uniquely identify every national region where clocks have all 228 agreed since 1970. This is essential for the intended use: static 229 clocks keeping local civil time. 230 231 * Indicate to humans as to where that region is. This simplifes use. 232 233 * Be robust in the presence of political changes. This reduces the 234 number of updates and backward-compatibility hacks. For example, 235 names of countries are ordinarily not used, to avoid 236 incompatibilities when countries change their name 237 (e.g. Zaire->Congo) or when locations change countries 238 (e.g. Hong Kong from UK colony to China). 239 240 * Be portable to a wide variety of implementations. 241 This promotes use of the technology. 242 243 * Use a consistent naming convention over the entire world. 244 This simplifies both use and maintenance. 245 246This naming convention is not intended for use by inexperienced users 247to select TZ values by themselves (though they can of course examine 248and reuse existing settings). Distributors should provide 249documentation and/or a simple selection interface that explains the 250names; see the 'tzselect' program supplied with this distribution for 251one example. 252 253Names normally have the form AREA/LOCATION, where AREA is the name 254of a continent or ocean, and LOCATION is the name of a specific 255location within that region. North and South America share the same 256area, `America'. Typical names are `Africa/Cairo', `America/New_York', 257and `Pacific/Honolulu'. 258 259Here are the general rules used for choosing location names, 260in decreasing order of importance: 261 262 Use only valid POSIX file name components (i.e., the parts of 263 names other than `/'). Within a file name component, 264 use only ASCII letters, `.', `-' and `_'. Do not use 265 digits, as that might create an ambiguity with POSIX 266 TZ strings. A file name component must not exceed 14 267 characters or start with `-'. E.g., prefer `Brunei' 268 to `Bandar_Seri_Begawan'. 269 Include at least one location per time zone rule set per country. 270 One such location is enough. Use ISO 3166 (see the file 271 iso3166.tab) to help decide whether something is a country. 272 However, uninhabited ISO 3166 regions like Bouvet Island 273 do not need locations, since local time is not defined there. 274 If all the clocks in a country's region have agreed since 1970, 275 don't bother to include more than one location 276 even if subregions' clocks disagreed before 1970. 277 Otherwise these tables would become annoyingly large. 278 If a name is ambiguous, use a less ambiguous alternative; 279 e.g. many cities are named San Jose and Georgetown, so 280 prefer `Costa_Rica' to `San_Jose' and `Guyana' to `Georgetown'. 281 Keep locations compact. Use cities or small islands, not countries 282 or regions, so that any future time zone changes do not split 283 locations into different time zones. E.g. prefer `Paris' 284 to `France', since France has had multiple time zones. 285 Use mainstream English spelling, e.g. prefer `Rome' to `Roma', and 286 prefer `Athens' to the true name (which uses Greek letters). 287 The POSIX file name restrictions encourage this rule. 288 Use the most populous among locations in a country's time zone, 289 e.g. prefer `Shanghai' to `Beijing'. Among locations with 290 similar populations, pick the best-known location, 291 e.g. prefer `Rome' to `Milan'. 292 Use the singular form, e.g. prefer `Canary' to `Canaries'. 293 Omit common suffixes like `_Islands' and `_City', unless that 294 would lead to ambiguity. E.g. prefer `Cayman' to 295 `Cayman_Islands' and `Guatemala' to `Guatemala_City', 296 but prefer `Mexico_City' to `Mexico' because the country 297 of Mexico has several time zones. 298 Use `_' to represent a space. 299 Omit `.' from abbreviations in names, e.g. prefer `St_Helena' 300 to `St._Helena'. 301 Do not change established names if they only marginally 302 violate the above rules. For example, don't change 303 the existing name `Rome' to `Milan' merely because 304 Milan's population has grown to be somewhat greater 305 than Rome's. 306 If a name is changed, put its old spelling in the `backward' file. 307 308The file `zone.tab' lists the geographical locations used to name 309time zone rule files. It is intended to be an exhaustive list 310of canonical names for geographic regions. 311 312Older versions of this package used a different naming scheme, 313and these older names are still supported. 314See the file `backward' for most of these older names 315(e.g. `US/Eastern' instead of `America/New_York'). 316The other old-fashioned names still supported are 317+`WET', `CET', `MET', and `EET' (see the file `europe'). 318 319 320----- Time zone abbreviations ----- 321 322When this package is installed, it generates time zone abbreviations 323like `EST' to be compatible with human tradition and POSIX. 324Here are the general rules used for choosing time zone abbreviations, 325in decreasing order of importance: 326 327 Use abbreviations that consist of three or more ASCII letters. 328 Previous editions of this database also used characters like 329 ' ' and '?', but these characters have a special meaning to 330 the shell and cause commands like 331 set `date` 332 to have unexpected effects. 333 Previous editions of this rule required upper-case letters, 334 but the Congressman who introduced Chamorro Standard Time 335 preferred "ChST", so the rule has been relaxed. 336 337 This rule guarantees that all abbreviations could have 338 been specified by a POSIX TZ string. POSIX 339 requires at least three characters for an 340 abbreviation. POSIX through 2000 says that an abbreviation 341 cannot start with ':', and cannot contain ',', '-', 342 '+', NUL, or a digit. POSIX from 2001 on changes this 343 rule to say that an abbreviation can contain only '-', '+', 344 and alphanumeric characters from the portable character set 345 in the current locale. To be portable to both sets of 346 rules, an abbreviation must therefore use only ASCII 347 letters. 348 349 Use abbreviations that are in common use among English-speakers, 350 e.g. `EST' for Eastern Standard Time in North America. 351 We assume that applications translate them to other languages 352 as part of the normal localization process; for example, 353 a French application might translate `EST' to `HNE'. 354 355 For zones whose times are taken from a city's longitude, use the 356 traditional xMT notation, e.g. `PMT' for Paris Mean Time. 357 The only name like this in current use is `GMT'. 358 359 If there is no common English abbreviation, abbreviate the English 360 translation of the usual phrase used by native speakers. 361 If this is not available or is a phrase mentioning the country 362 (e.g. ``Cape Verde Time''), then: 363 364 When a country has a single or principal time zone region, 365 append `T' to the country's ISO code, e.g. `CVT' for 366 Cape Verde Time. For summer time append `ST'; 367 for double summer time append `DST'; etc. 368 When a country has multiple time zones, take the first three 369 letters of an English place name identifying each zone 370 and then append `T', `ST', etc. as before; 371 e.g. `VLAST' for VLAdivostok Summer Time. 372 373 Use UTC (with time zone abbreviation "zzz") for locations while 374 uninhabited. The "zzz" mnemonic is that these locations are, 375 in some sense, asleep. 376 377Application writers should note that these abbreviations are ambiguous 378in practice: e.g. `EST' has a different meaning in Australia than 379it does in the United States. In new applications, it's often better 380to use numeric UTC offsets like `-0500' instead of time zone 381abbreviations like `EST'; this avoids the ambiguity. 382 383 384----- Calendrical issues ----- 385 386Calendrical issues are a bit out of scope for a time zone database, 387but they indicate the sort of problems that we would run into if we 388extended the time zone database further into the past. An excellent 389resource in this area is Nachum Dershowitz and Edward M. Reingold, 390<a href="http://emr.cs.iit.edu/home/reingold/calendar-book/third-edition/"> 391Calendrical Calculations: Third Edition 392</a>, Cambridge University Press (2008). Other information and 393sources are given below. They sometimes disagree. 394 395 396France 397 398Gregorian calendar adopted 1582-12-20. 399French Revolutionary calendar used 1793-11-24 through 1805-12-31, 400and (in Paris only) 1871-05-06 through 1871-05-23. 401 402 403Russia 404 405From Chris Carrier (1996-12-02): 406On 1929-10-01 the Soviet Union instituted an ``Eternal Calendar'' 407with 30-day months plus 5 holidays, with a 5-day week. 408On 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the 409Gregorian calendar while retaining the 6-day week; on 1940-06-27 it 410reverted to the 7-day week. With the 6-day week the usual days 411off were the 6th, 12th, 18th, 24th and 30th of the month. 412(Source: Evitiar Zerubavel, _The Seven Day Circle_) 413 414 415Mark Brader reported a similar story in "The Book of Calendars", edited 416by Frank Parise (1982, Facts on File, ISBN 0-8719-6467-8), page 377. But: 417 418From: Petteri Sulonen (via Usenet) 419Date: 14 Jan 1999 00:00:00 GMT 420... 421 422If your source is correct, how come documents between 1929 -- 1940 were 423still dated using the conventional, Gregorian calendar? 424 425I can post a scan of a document dated December 1, 1934, signed by 426Yenukidze, the secretary, on behalf of Kalinin, the President of the 427Executive Committee of the Supreme Soviet, if you like. 428 429 430 431Sweden (and Finland) 432 433From: Mark Brader 434<a href="news:1996Jul6.012937.29190@sq.com"> 435Subject: Re: Gregorian reform -- a part of locale? 436</a> 437Date: 1996-07-06 438 439In 1700, Denmark made the transition from Julian to Gregorian. Sweden 440decided to *start* a transition in 1700 as well, but rather than have one of 441those unsightly calendar gaps :-), they simply decreed that the next leap 442year after 1696 would be in 1744 -- putting the whole country on a calendar 443different from both Julian and Gregorian for a period of 40 years. 444 445However, in 1704 something went wrong and the plan was not carried through; 446they did, after all, have a leap year that year. And one in 1708. In 1712 447they gave it up and went back to Julian, putting 30 days in February that 448year!... 449 450Then in 1753, Sweden made the transition to Gregorian in the usual manner, 451getting there only 13 years behind the original schedule. 452 453(A previous posting of this story was challenged, and Swedish readers 454produced the following references to support it: "Tiderakning och historia" 455by Natanael Beckman (1924) and "Tid, en bok om tiderakning och 456kalendervasen" by Lars-Olof Lode'n (no date was given).) 457 458 459Grotefend's data 460 461From: "Michael Palmer" [with one obvious typo fixed] 462Subject: Re: Gregorian Calendar (was Re: Another FHC related question 463Newsgroups: soc.genealogy.german 464Date: Tue, 9 Feb 1999 02:32:48 -800 465... 466 467The following is a(n incomplete) listing, arranged chronologically, of 468European states, with the date they converted from the Julian to the 469Gregorian calendar: 470 47104/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman 472 Catholics and Danzig only) 47309/20 Dec 1582 - France, Lorraine 474 47521 Dec 1582/ 476 01 Jan 1583 - Holland, Brabant, Flanders, Hennegau 47710/21 Feb 1583 - bishopric of Liege (L"uttich) 47813/24 Feb 1583 - bishopric of Augsburg 47904/15 Oct 1583 - electorate of Trier 48005/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg, 481 Salzburg, Brixen 48213/24 Oct 1583 - Austrian Oberelsass and Breisgau 48320/31 Oct 1583 - bishopric of Basel 48402/13 Nov 1583 - duchy of J"ulich-Berg 48502/13 Nov 1583 - electorate and city of K"oln 48604/15 Nov 1583 - bishopric of W"urzburg 48711/22 Nov 1583 - electorate of Mainz 48816/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden 48917/28 Nov 1583 - bishopric of M"unster and duchy of Cleve 49014/25 Dec 1583 - Steiermark 491 49206/17 Jan 1584 - Austria and Bohemia 49311/22 Jan 1584 - Luzern, Uri, Schwyz, Zug, Freiburg, Solothurn 49412/23 Jan 1584 - Silesia and the Lausitz 49522 Jan/ 496 02 Feb 1584 - Hungary (legally on 21 Oct 1587) 497 Jun 1584 - Unterwalden 49801/12 Jul 1584 - duchy of Westfalen 499 50016/27 Jun 1585 - bishopric of Paderborn 501 50214/25 Dec 1590 - Transylvania 503 50422 Aug/ 505 02 Sep 1612 - duchy of Prussia 506 50713/24 Dec 1614 - Pfalz-Neuburg 508 509 1617 - duchy of Kurland (reverted to the Julian calendar in 510 1796) 511 512 1624 - bishopric of Osnabr"uck 513 514 1630 - bishopric of Minden 515 51615/26 Mar 1631 - bishopric of Hildesheim 517 518 1655 - Kanton Wallis 519 52005/16 Feb 1682 - city of Strassburg 521 52218 Feb/ 523 01 Mar 1700 - Protestant Germany (including Swedish possessions in 524 Germany), Denmark, Norway 52530 Jun/ 526 12 Jul 1700 - Gelderland, Zutphen 52710 Nov/ 528 12 Dec 1700 - Utrecht, Overijssel 529 53031 Dec 1700/ 531 12 Jan 1701 - Friesland, Groningen, Z"urich, Bern, Basel, Geneva, 532 Turgau, and Schaffhausen 533 534 1724 - Glarus, Appenzell, and the city of St. Gallen 535 53601 Jan 1750 - Pisa and Florence 537 53802/14 Sep 1752 - Great Britain 539 54017 Feb/ 541 01 Mar 1753 - Sweden 542 5431760-1812 - Graub"unden 544 545The Russian empire (including Finland and the Baltic states) did not 546convert to the Gregorian calendar until the Soviet revolution of 1917. 547 548Source: H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen 549Mittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend 550(Hannover: Hahnsche Buchhandlung, 1941), pp. 26-28. 551 552 553----- Time and time zones on Mars ----- 554 555Some people have adjusted their work schedules to fit Mars time. 556Dozens of special Mars watches were built for Jet Propulsion 557Laboratory workers who kept Mars time during the Mars Exploration 558Rovers mission (2004). These timepieces look like normal Seikos and 559Citizens but use Mars seconds rather than terrestrial seconds. 560 561A Mars solar day is called a "sol" and has a mean period equal to 562about 24 hours 39 minutes 35.244 seconds in terrestrial time. It is 563divided into a conventional 24-hour clock, so each Mars second equals 564about 1.02749125 terrestrial seconds. 565 566The prime meridian of Mars goes through the center of the crater 567Airy-0, named in honor of the British astronomer who built the 568Greenwich telescope that defines Earth's prime meridian. Mean solar 569time on the Mars prime meridian is called Mars Coordinated Time (MTC). 570 571Each landed mission on Mars has adopted a different reference for 572solar time keeping, so there is no real standard for Mars time zones. 573For example, the Mars Exploration Rover project (2004) defined two 574time zones "Local Solar Time A" and "Local Solar Time B" for its two 575missions, each zone designed so that its time equals local true solar 576time at approximately the middle of the nominal mission. Such a "time 577zone" is not particularly suited for any application other than the 578mission itself. 579 580Many calendars have been proposed for Mars, but none have achieved 581wide acceptance. Astronomers often use Mars Sol Date (MSD) which is a 582sequential count of Mars solar days elapsed since about 1873-12-29 58312:00 GMT. 584 585The tz database does not currently support Mars time, but it is 586documented here in the hopes that support will be added eventually. 587 588Sources: 589 590Michael Allison and Robert Schmunk, 591"Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock" 592<http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2004-07-30). 593 594Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times 595(2004-01-14), pp A1, A20-A21. 596