Tz database
The timezone database ( engl: tz database, IANA timezone database or zoneinfo database) is an IANA database contains information on the time zones of the world. Primarily it is intended for use in computer programs and operating systems. It is sometimes also called Olson database, after the founding member Arthur David Olson. Paul Eggert is an editor and performs the database.
The most notable feature is Paul Eggert uniform naming scheme for time zones, such as " America / New_York" ( America / New_York, English ) and " Europe / Paris" ( Europe / Paris, English). The database tried all historical time zones and all changes civilian time since 1970, the Unix time epoch recorded. This includes changing between summer and winter time and even leap seconds.
- 4.1 zone.tab
History
The origins go back to at least the year 1986. The database of the project, as well as parts of the source code used, are in the public domain. The Modernity maintenance several times a year a new version of the database is usually published.
Definition of a time zone
The timezone database to define a time zone from the common understanding differs. The database provides each national or regional territory as time zone in the show all watches since 1970 officially the same time and have any changes been through together. First and foremost, this definition thus describes geographic areas that had continually a uniform time. This differs from other definitions, emanating from a single deviation from the zero meridian. In contrast, the time zone database to assign each time zone several different variations on the coordinated world time, typically winter time and summer time is listed in the file of a zone.
The names of the time zones
To make them easier to understand for people who have time zones unique names in the form " Area / Location ," for example, " America / New_York" ( "America / New_York", English). It was also decided to use English names or their transcriptions and omit punctuation, and common suffixes. Instead of blank firing underscores be used. Hyphens are used as usual.
Area
Area is either the name of a continent, an ocean or simply " Etc ". At the continents and oceans are currently Africa ( Africa), America (America), Antarctica ( Antarctica ), Arctic ( the Arctic Ocean ), Asia (Asia), Atlantic ( the Atlantic ), Australia ( Australia), Europe (Europe), Indian ( Indian Ocean ) and Pacific ( the Pacific) counted.
The specialty of " Etc. " is used for some administrative zones, particularly for " Etc / UTC " Coordinated Universal Time. For compatibility with the POSIX format are the zones that begin with " Etc / GMT", exactly the opposite sign as you would expect. In this format, all areas of the west GMT have a positive sign and all east of it negative.
Place
Location is the name of a specific place within the region, usually a city or a small island. Country names are not used in this scheme, mainly because they are not stable over time due to political changes and border changes. The names of large cities are more permanent. Nevertheless, the employees of the database time zone per ISO least try to insert 3166-1 alpha -2 country code and some user interfaces make them even use. In addition, there is an interest in that places are kept geographically compact, so that any changes in time zones divide no places in different time zones.
Usually, the most populous city of a region is selected for naming the entire time zone, other cities come to train, if they are known or have clearer names. The name of a city should change once the deal is that henceforth an alias would be used and refer both names for the same database entry.
Stored data is a time zone
As each time zone has several variations, mostly winter and summer time, records the time zone database the exact time of each change on. The format thus also takes changes in the date and time the time change itself true.
Zone.tab
The zone.tab file under is legally public domain. Rows and columns are described in the comments of the files as follows:
# This file contains a table with columns the Following: # 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 format sign- degrees -minutes -seconds, # 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 in order within the country did # (1 ) makes some geographical sense, and # (2 ) puts the most populous zones first, where did does not contradict (1). Data from before 1970
When data from before 1970 is trying to keep it for the city, which defines the region, correct, but they are not always applicable to the entire region. This is because regions can only be divided when there has been the official time differences since 1970.
In Brazil, for example, alternated between October 23 and December 9, 1963, only the regions around Minas Gerais, Espirito Santo, Rio de Janeiro and São Paulo to summer time. A request that region, " America / Sao_Paulo " ( "America / Sao Paulo ", English ) to share, but was rejected because the clocks are identical throughout the region since 1970. The German time zone " Europe / Berlin " ( "Europe / Berlin", English ) is, for example, incorrect for the period after 1945, when the Berlin trizone changing to daylight saving time did not cooperate.