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Sources for Time Zone and Daylight Saving Time DataSources for Time Zone and Daylight Saving Time Data@(#)tz-link.htm 8.15Please send corrections to this web page to thetime zone mailing list.The tz databaseThe public-domaintime zone database contains code and datathat represent the history of local timefor many representative locations around the globe.It is updated periodically to reflect changes made by political bodiesto time zoneboundaries, UTC offsets, anddaylight-savingrules.This database (often called tz or zoneinfo)is used by several implementations,includingtheGNUC Library used inGNU/Linux,FreeBSD,NetBSD,OpenBSD,Cygwin,DJGPP,AIX,Mac OS X,OpenVMS,Oracle Database,Solaris,Tru64, andUnixWare.Each location in the database represents a national region where allclocks keeping local time have agreed since 1970.Locations are identified by continent or ocean and then by the name ofthe location, which is typically the largest city within the region.For example, America/New_Yorkrepresents most of the US eastern time zone;America/Phoenix represents most of Arizona, whichuses mountain time without daylight saving time (DST);America/Detroit represents most of Michigan, which useseastern time but with different DST rules in 1975;and other entries represent smaller regions like Starke County,Indiana, which switched from central to eastern time in 1991and switched back in 2006.To use the database on an extended POSIXimplementation set the TZ environment variable tothe location's full name, e.g., TZ="America/New_York".In the tz database'sFTP distributionthe code is in the file tzcodeC.tar.gz,where C is the code's version;similarly, the data are in tzdataD.tar.gz,where D is the data's version.The following shell commands downloadthese files to a GNU/Linux or similar host;see the downloadedREADME file for what to do next.wget 'ftp://elsie.nci.nih.gov/pub/tz*.tar.gz'gzip -dc tzcode*.tar.gz | tar -xf -gzip -dc tzdata*.tar.gz | tar -xf -The code lets you compile the tz source files intomachine-readable binary files, one for each location. It also letsyou read a tz binary file and interpret time stamps for thatlocation.The data are by no means authoritative. If you find errors, pleasesend changes to the time zonemailing list. You can also browse recentmessages sent to the mailing list, subscribe to it,retrieve the full archive of oldmessages (in gzip compressed format), or retrieve archived older versions of codeand data; there is also a smaller HTTPmirror.The Web has several other sources for time zone and daylight saving time data.Here are some recent links that may be of interest.Web pages using recent versions of the tz databaseThese are listed roughly in ascending order of complexity and fanciness.Date and Time Gatewaylets you see the TZ values directly.CurrentTime in 1000 Places uses descriptions of the values.Time Zone Converteruses a pulldown menu.Completetimezone information for all countries displays tables of DST rules.The World Clock -Time Zones lets you sort zone names and convert times.Graphical Display ofTime Zones and Daylight Saving Times shows a graph of timedifference versus time for any pair of locations.The World Time Enginealso contains data about time zone boundaries; it supports queries via placenames and shows location maps.Other time zone database formatsThe Internet Calendaring and Scheduling Core Object Specification(iCalendar), Internet RFC 2445, published by the (now-concluded) IETFCalendaring and Scheduling Working Group (calsch)covers time zonedata; see its VTIMEZONE calendar component.The Calendaring and SchedulingConsortium is promoting further work in this area. iCalendarTIMEZONE Problems and Recommendations offers guidelines andrecommendations for the use of VTIMEZONE and tz.Extended DaylightSaving Time Links, Advisories and Changes lists vendor material on recentdaylight saving time changes.TimezoneRegistry and Service Recommendations discusses astrategy for defining and deploying a time zoneregistration process that would establish unique names for eachversion of each tz zone, along with a polygonalrepresentation of the geographical area corresponding to thezone.The www-rdf-calendarlist discusses RDF-based calendarand group scheduling systems, and has a workspace on time zonedata converted from tz. An earlier schema was sketched out.Other tz compilersVzic iCalendarTimezone Converter describes a Cprogram that compilestz source into iCalendar-compatible VTIMEZONE files.Vzic is freelyavailable under the GNUGeneral Public License (GPL).tziCal - tzdatabase conversion utility is like Vzic, except for the .NET framework.DateTime::TimeZonecontains a script parse_olson that compilestz source into Perlmodules. It is part of the Perl DateTime Project, which is freelyavailable under both the GPL and the Perl ArtisticLicense. DateTime::TimeZone also contains a scripttests_from_zdump that generates test cases for each clocktransition in the tz database.International Components forUnicode (ICU) contains C/C++ and Javalibraries for internationalization thathas a compiler from tz sourceinto an ICU-specific format.ICU is freely available under aBSD-style license.Joda Time - Java dateand time APIcontains a classorg.joda.time.tz.ZoneInfoCompiler that compilestz source into a Joda-specific binary format. Joda Timeis freely available under a BSD-style license.PyTZ - Python TimeZone Library compiles tz source intoPython.It is freely available under a BSD-style license.TZInfo - Ruby Timezone Librarycompiles tz source intoRuby.It is freely available under the MIT license.The Chronos Date/TimeLibrary is a Smalltalk classlibrary that compiles tz source into a time zone repository whose formatis either proprietary or an XML-encodedrepresentation.Starting with version 8.5, Tclcontains a developer-oriented parser that compiles tzsource into text files, along with a runtime that can read thosefiles. Tcl is freely available under a BSD-stylelicense.Other tz binary file readersThe GNU CLibraryhas an independent, thread-safe implementation ofa tz binary file reader.This library is freely available under theGNU Lesser General Public License(LGPL),and is widely used in GNU/Linux systems.ZoneInfo.javais a tz binary file reader written in Java.It is freely available under the LGPL.Tcl, mentioned above, also contains atz binary file reader.Other tz-based time zone softwareFoxClocksis an extension for MozillaToolkit applications like Firefox, Thunderbird, andSunbird.It displays multiple clocks in the application window, and has a mappinginterface to Google Earth.It is freely available under the GPL.Internationalclock (intclock) is a multi-timezone clock forGNU/Linux and similar systems. It is freely availableunder the GPL.PublicDomainhas a copy of a recent tz database, accessed via a C# library. As itsname suggests, it is in the public domain. Only current time stampsare well supported; historical data are compiled into the runtime butare not easily accessible.Sun Java releases since 1.4contain a copy of a subset of a recent tz database in aJava-specific format.Time Zone isa WordPress plugin. It is freelyavailable under a BSD-style license.VelaTerra isa Mac OS X program. Its developersoffer freelicenses to tz contributors.World Time Explorer is aMicrosoft Windows program.Other time zone databasesAtlas Queryis Astrodienst's Web version of Shanks'sexcellent time zone history atlases published in both computerand book form (one volumefor the USA, and one forother locations) by Astro Communications Services.WORLDTIME: interactive atlas,time info, public holidayscontains information on local time, sunrise and sunset,and public holidays in several hundred cities around the world.World Time Serveris another time zone database.World Time Zonescontains data from the Time Service Department of theUS Naval Observatory, used as the sourcefor the usno* files in the tz distribution.The StandardSchedules Information Manual of theInternational Air TransportAssociationgives current time zone rules for airports served by commercial aviation.Some Microsoft Windows versions contain time zone information inan undocumented format, with IDs that can be mapped to TZvalues using the Windows→ Tzid table maintained by the CLDR data mentionedbelow.MapsThe United States CentralIntelligence Agency (CIA) publishes a timezone map; thePerry-CastañedaLibrary Map Collectionof the University of Texas at Austin has copies ofrecent editions.The pictorial quality is good,but the maps do not indicate summer time,and parts of the data are a few years out of date.Current time around the worldand standard time zones map of the worldhas several fancy time zone maps; it covers Russia particularly well.The maps' pictorial quality is not quite as good as theCIA'sbut the maps are more up to date.Time zone boundariesA map of the TZ timezones inthe US contains a shapefile of thetz regions in the US.Administrative Divisionsof Countries ("Statoids") contains detailed lists oftz-related zone subdivision data.Timezone boundaries for multizone countries summarizes legalboundaries between time zones within countries.Manifold.net's Free Maps andGISData includes a Manifold-format map ofworld time zone boundaries distributed under theGPL.The US Geological Survey's National Atlas ofthe United Statespublishes the TimeZones of the United States in the public domain.The GeoCommunity lists several commercial sources for InternationalTime Zones and Time Zone Data.A ship within the territorialwaters of any nation uses that nation's time. In internationalwaters, time zone boundaries are meridians 15° apart, except thatUTC−12 and UTC+12 are each 7.5° wide and are separated bythe 180° meridian (not by the International Date Line, which isfor land and territorial waters only). A captain can change ship'sclocks any time after entering a new time zone; midnight changes arecommon.Civil time concepts and historyAWalk through Timesurveys the evolution of timekeeping.About DaylightSaving Time - History, rationale, laws & datesis an overall history of DST.Saving Time,Saving Energy discusses a primary justification for DST.Who Knew? A BriefHistory of Daylight Saving Time summarizes some of the contentioushistory of DST.TheTime of Internetdescribes time zones and daylight saving time,with diagrams.The time zone map is out of date, however.A History ofthe International Date Line tells the story of the most importanttime zone boundary.Basic TimeZone Concepts discusses terminological issues behind time zones.National histories of legal timeAustraliaThe Parliamentary Library has commissioned researchnote on daylight saving time in Australia.The Bureau of Meteorology publishes a list ofImplementation Dates of Daylight Savings Time within Australia.BelgiumThe Royal Observatory of Belgium maintains a table of time in Belgium (in Dutch).BrazilThe Time Service Department of the National Observatoryrecords Brazil's daylight saving time decrees (inPortuguese).CanadaThe Institute for National Measurement Standards publishes currentand some older information about TimeZones & Daylight Saving Time.ChileThe Chilean Hydrographic and Oceanographic Service publishes a history ofofficial time (in Spanish).GermanyThe National Institute for Science and Technology maintains the Realisation ofLegal Time in Germany.IsraelThe Interior Ministry periodically issues announcements (in Hebrew).MexicoThe Investigation and Analysis Service of the Mexican Library ofCongress has published a history of Mexican local time (in Spanish).MalaysiaSee Singapore below.NetherlandsLegal time in the Netherlands (in Dutch)covers the history of local time in the Netherlands from ancient times.New ZealandThe Department of Internal Affairs maintains a brief history AboutDaylight Saving. The privately-maintained History of New Zealandtime has more details.NorwayThe Norwegian Meteorological Institute listsSummertime in Norway (in Norwegian), citing theInstitute of Theoretical Astrophysics, Oslo.SingaporeWhyis Singapore in the "Wrong" Time Zone? details thehistory of legal time in Singapore and Malaysia.United KingdomHistory oflegal time in Britain discusses in detail the countrywith perhaps the best-documented history of clock adjustments.The National Physical Laboratory also maintains an Archiveof Summer time dates.Precision timekeepingTheScience of Timekeeping is a thorough introductionto the theory and practice of precision timekeeping.NTP: The NetworkTime Protocoldiscusses how to synchronize clocks ofInternet hosts.TimezoneOptions for DHCP(Internet RFC 4833)specifies a DHCP option for a server to configurea client's time zone and daylight saving settings automatically.A FewFacts Concerning GMT, UT, andthe RGOanswers questions like "What is thedifference between GMT and UTC?"AstronomicalTimes explains more abstruse astronomical time scales likeTDT,TCG, andTDB.TimeScales goes into more detail, particularly for historical variants.The IAU's SOFAinitiative publishes Fortrancode for converting among time scales likeTAI,TDB, TDT andUTC.Basics ofSpace Flight - Reference Systems - Time Conventionsbriefly explains interplanetary space flight timekeeping.TechnicalNotes on Mars Solar Time as Adopted by the Mars24 Sunclock brieflydescribes Mars Coordinated Time (MTC) and thediverse local timescales used by each landed mission on Mars.LeapSecond.com isdedicated not only to leap seconds but to precise time and frequencyin general. It covers the state of the art in amateur timekeeping, andhow the art has progressed over the past few decades.Bulletinsmaintained by theIERSEOP(PC) contains official publications ofthe Earth Orientation Parameters Product Center of theInternational Earth Rotation Service, the committee that decideswhen leap seconds occur.The LeapSecond Discussion List covers McCarthyand Klepczynski's proposal to discontinue leap seconds,discussed further inTheleap second: its history and possible future.The AAS Leap SecondCommittee has solicited input on this proposal.TheFuture of Leap Seconds covers thiscontentious issue.Time notationA Summary ofthe International Standard Date and Time Notation is a goodsummary ofISO8601:2004 -- Data elements and interchange formats -- Informationinterchange -- Representation of dates and times.XMLSchema: Datatypes - dateTime specifies a format inspired byISO 8601 that is in common use in XML data.InternetMessage Format (Internet RFC 2822) §3.3specifies the time notation used in email and HTTPheaders.Date and Timeon the Internet: Timestamps (Internet RFC 3339)specifies an ISO 8601profile for use in new Internetprotocols.Date & TimeFormats on the Web surveys web- and Internet-oriented date and timeformats.TheBest of Dates, the Worst of Dates covers many problems encounteredby software developers when handling dates and time stamps.The Unicode Common Locale Data Repository(CLDR) Project has localizations for time zone names,abbreviations, identifiers, and formats. For example, it containsFrench translations for "Eastern European Summer Time", "EEST", and"Bucharest". By-TypeChart: names.metazone shows these values for many locales.ICU contains a mechanism for using this data.Alphabetic time zone abbreviations should not be used as uniqueidentifiers for UTC offsets as they are ambiguous inpractice. For example, "EST" denotes 5 hours behindUTC in English-speaking North America, but it denotes 10or 11 hours ahead of UTC in Australia; andFrench-speaking North Americans prefer"HNE" to"EST". For POSIX the tzdatabase contains English abbreviations for all time stamps but inmany cases these are merely inventions of the databasemaintainers.Numeric time zone abbreviations typically count hours east ofUTC, e.g., +09 for Japan and-10 for Hawaii. However, the POSIXTZ environment variable uses the opposite convention. Forexample, one might use TZ="JST-9" andTZ="HST10" for Japan and Hawaii, respectively. If thetz database is available, it is usually better to usesettings like TZ="Asia/Tokyo" andTZ="Pacific/Honolulu" instead, as this should avoidconfusion, handle old time stamps better, and insulate you better fromany future changes to the rules. One should never setPOSIX TZ to a value like"GMT-9", though, since this would falsely claim thatlocal time is nine hours ahead of UTC and the time zoneis called "GMT".Related indexesTime and the ArtsOpen Directory -Reference: TimeGoogle Directory- Reference > TimeYahoo!Directory > Science > Measurements and Units > Time |
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