Time zone database

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The timezone database ( English: tz database , IANA timezone database or zoneinfo database ) is a database of IANA , the information on the time zone contains the earth. It is primarily intended for use in application programs and operating systems. It is sometimes called the Olson database after founding member Arthur David Olson. Paul Eggert is editor and runs the database.

The most notable feature is Paul Eggert's uniform naming for time zones, such as "America / New_York" (America / New_York, English ) and "Europe / Paris" (Europe / Paris, English ). The database tries to record all historical time zones and all changes in civil time since 1970, the Unix era. This also includes changes between summer and winter time and even leap seconds .

The time zone database divides the world into regions where all local clocks have shown the same time since 1970. This map, updated to 2009, includes data from all regions except Antarctica.

history

The origins go back to at least 1986. The project database and parts of the source code used are in the public domain . In order to keep it up-to-date, a new version of the database is usually published several times a year.

Definition of a time zone

In the time zone database, the definition of a time zone differs from general understanding. The database sees every national or regional area as a time zone in which all clocks officially show the same time since 1970 and have participated in every change. First and foremost, this definition describes geographical areas that continuously had a uniform time. This differs from other definitions that assume a uniform deviation from the prime meridian . In contrast to this, the time zone database can assign several different deviations from the coordinated universal time to each time zone ; winter time and daylight saving time are typically listed in the file for a zone.

The naming of the time zones

To make them easier for people to understand, the time zones have unique names in the form of " Territory / Location ", for example "America / New_York" ("Amerika / New_York", English ). It was also decided to use English names or transcriptions and to leave out punctuation and common suffixes. Instead of blank firing are underscores used. Hyphens are used as usual.

area

Territory is either the name of a continent, an ocean, or simply "etc". Africa ( Africa ), America ( America ), Antarctica ( Antarctica ), Arctic (the Arctic Sea ), Asia ( Asia ), Atlantic (the Atlantic ), Australia ( Australia ), Europe ( Europe ) and Indian are currently becoming continents and oceans (the Indian Ocean ) and Pacific (the Pacific ).

The specialty "Etc" is used for some administrative zones, in particular for "Etc / UTC", the coordinated universal time . For compatibility with the POSIX format, the zones that begin with "Etc / GMT" have exactly the opposite sign than one would expect. In this format, all zones west of GMT have a positive sign and all zones east of it have a negative sign.

place

Place is the name of a specific place within the region, usually a town or a small island. Country names are not used in this scheme, mainly because they are not time-stable due to political changes and border changes; the names of big cities tend to be permanent. Nevertheless, the employees of the database try to insert at least one time zone per ISO 3166-1 alpha-2 country code, and some user interfaces make use of it. In addition, there is an interest in keeping locations geographically compact so that any changes to time zones do not split locations into different time zones.

Usually the most populous city in a region is chosen to name the entire time zone, with other cities also being considered if they are better known or have clearer names. Should the name of a city change, the agreement is that from now on an alias name would be used and both names would refer to the same database entry.

Saved data for a time zone

Since every time zone has different deviations, usually winter and summer time , the time zone database records the exact time of each change. The format also recognizes changes in the date and time of the time change itself.

Zone.tab

The zone.tab file is legally subject to the public domain . Lines and columns are described in the comment of the files as follows: 

# This file contains a table with the following columns:
# 1. ISO 3166 2-character country code. See the file `iso3166.tab'.
# 2. Latitude and longitude of the zone's principal location
#     in ISO 6709 sign-degrees-minutes-seconds format,
#     either +-DDMM+-DDDMM or +-DDMMSS+-DDDMMSS,
#     first latitude (+ is north), then longitude (+ is east).
# 3. Zone name used in value of TZ environment variable.
# 4. Comments; present if and only if the country has multiple rows.
#
# Columns are separated by a single tab.
# The table is sorted first by country, then an order within the country that
# (1) makes some geographical sense, and
# (2) puts the most populous zones first, where that does not contradict (1).

Data from before 1970

For data from before 1970 an attempt is made to hold it correct for the city that defines the region. However, they are not always applicable for the entire region, because regions are only divided up in the database if there have been differences in the official time since 1970.

In Brazil, for example, between October 23 and December 9, 1963, only the regions around Minas Gerais , Espírito Santo , Rio de Janeiro and São Paulo switched to daylight saving time. A request to split up the “America / Sao_Paulo” region (“America / São Paulo”, English ) was refused because the clocks have been running identically in the entire region since 1970. For example, the German time zone, "Europe / Berlin" ("Europa / Berlin", English ) is not correct for the period after 1945, when the Trizone Berlin did not make the switch to summer time.

Web links

Individual evidence

  1. ^ Paul Eggert, Olson, Arthur David: Sources for time zone and daylight saving time data (sources for time zone and daylight saving time data, English ) . November 29, 2007. Retrieved December 3, 2007.
  2. ^ Paul Eggert: Re: FW: IANA time zone registration - proposal (Re: FW: IANA time zone registration proposal, English ) . January 2005. Archived from the original on September 27, 2011. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved July 30, 2011. @1@ 2Template: Webachiv / IABot / osdir.com
  3. ↑ Mueller, Erik: A map of the TZ timezones of the world (A map of the time zones of the world, according to the time zone database, English ) . Retrieved July 30, 2011.
  4. ↑ zoneinfo tzcode and tzdata archives (FTP) (database code and data archives, English ) . Retrieved October 30, 2007.
  5. ↑ Theory (theory, text file in English ), included in the scope of the “tzcode” distribution. Reference to version tzcode2007h.tar.gz October 1, 2007
  6. ↑ cf. en: List of tz database time zones