IANA time zone database

IANA time zone database
Name	IANA time zone database
Othernames	tz database, zoneinfo, Olson database
Maintained by	Internet Assigned Numbers Authority
Initial release	1986
Latest release	ongoing
License	Public domain / permissive
Website	IANA time zone database

IANA time zone database is a compilation of data that maps historical and current civil timekeeping practices to named time zones used by many Unix-like operating systems, Linux, BSD, Mac OS X, Solaris, AIX, HP-UX and applications such as Java, PHP, Perl, Python, PostgreSQL, MySQL, Microsoft Windows (via synchronization), and Android. The database provides identifiers, rules, and offsets enabling software by Mozilla Foundation, Apple Inc., Google LLC, Oracle Corporation, Red Hat, Canonical and others to compute local civil time for historical dates, present use, and near-future transitions.

Overview

The database defines named time zones (e.g., region/city strings) and rule sets that represent offsets and daylight saving time transitions used by jurisdictions such as United Kingdom, United States, Germany, Russia, China, India, Japan, and Brazil. It records changes tied to events like the World War I wartime studies, World War II occupation adjustments, and legislative acts by entities including the United States Congress, European Parliament, Australian Parliament and municipal bodies such as New York City councils. Implementations use the data in libraries like tzdata packages, runtime components in glibc, musl, ICU, and wrappers such as zoneinfo modules to serve applications like PostgreSQL and services run by Amazon Web Services, Microsoft Azure, Google Cloud Platform.

History and development

Origins trace to individual efforts by computer scientists and contributors in the 1980s and 1990s, notably by Arthur David Olson and collaborators at institutions such as NCAR and later stewardship by organizations including the Internet Assigned Numbers Authority, Internet Engineering Task Force, and volunteer maintainers. The data evolved alongside standards like Coordinated Universal Time, conventions from the International Telecommunication Union, and epoch handling rooted in Unix time practices. Political events—treaties like Treaty of Versailles, reorganizations such as the dissolution of the Soviet Union, and international conferences like Conference on Security and Co-operation in Europe—have necessitated updates. Corporations including Sun Microsystems, IBM, Microsoft Corporation and free software communities have contributed patches, tests, and packaging.

Structure and contents

The database consists of text files: zone definitions, rule blocks, and link aliases. Each zone entry ties a location identifier—typically a continent/city pair referencing places such as Europe/London, America/New_York, Asia/Tokyo, Africa/Cairo and Pacific/Auckland—to base offsets and rule names. Rule blocks reference recurring transitions and historical one-off changes tied to legislation by bodies like the U.S. Congress or decisions by national agencies such as the National Institute of Standards and Technology. The archive includes source files, compiled binary forms used by glibc and zic (time zone compiler), and test suites employed by corporations like Google and projects such as OpenJDK.

Maintenance and governance

Maintenance is performed by a small team of volunteers coordinated with the Internet Assigned Numbers Authority and contributors from institutions including IETF participants, academic researchers, and engineers from Mozilla Foundation, Apple Inc., Google LLC, Red Hat, Oracle Corporation, and cloud providers like Amazon Web Services. Decisions follow conventions established in community discussion lists and patch review processes similar to those used by Linux kernel and other open source projects such as Apache Software Foundation projects. Upstream changes respond to announcements from national bodies such as the U.S. National Institute of Standards and Technology, the Office for National Statistics, and ministries in countries like Australia, Canada, Germany, and France.

Adoption and implementations

The database is packaged and distributed in operating system repositories for Debian, Ubuntu, Fedora, Arch Linux, FreeBSD, OpenBSD, and NetBSD, and integrated into runtime libraries for Java SE, ICU, and language runtimes for Ruby, Perl, Python, and Node.js. Cloud providers including Amazon Web Services, Google Cloud Platform, and Microsoft Azure rely on it to present correct timestamps in services consumed by enterprises such as Goldman Sachs, JPMorgan Chase, Walmart, and technology firms like Facebook (now Meta Platforms), Twitter (now X), and Netflix. Many standards organizations and protocols—IETF specifications, POSIX, and ISO bodies—interoperate with or reference the data as an authoritative source for civil time offsets.

Criticisms and limitations

Critiques include the reliance on volunteer maintainers which can create latency after sudden legislative changes by parliaments such as the Russian State Duma or decrees from presidents like those of France and Turkey; geopolitical disputes over place names involving territories like Crimea and regions affected by decisions of bodies such as the United Nations; and the complexity of encoding atypical local practices in entries for municipalities such as Lord Howe Island or special administrative regions like Hong Kong. Technical limitations noted by developers from Apple Inc., Google LLC, and the Free Software Foundation include the absence of machine-readable provenance metadata tied to parliamentary acts, challenges in representing nonstandard civil time systems, and occasional inconsistencies across packaged binaries in distributions like Debian and CentOS.

Category:Timekeeping