ISO 8601-2:2019

Overview

ISO 8601-2:2019 - "Date and time - Representations for information interchange - Part 2: Extensions" extends the base ISO 8601 rules to specify additional, standardized character-string representations of Gregorian calendar dates and 24-hour clock times for information interchange. It covers extended forms for uncertain or approximate dates, expanded time intervals, grouped time units, recurring intervals and simple date/time arithmetic. The standard is also applicable to times and time shifts based on Coordinated Universal Time (UTC). It explicitly excludes non‑Gregorian calendars, non‑24‑hour clocks and character encoding issues.

Key topics and technical requirements

• Extended date/time representations: additional explicit forms that build on ISO 8601-1, including expanded calendar years and unspecified digits.
• Uncertain/approximate dates: syntax for indicating uncertainty, approximation or partially unspecified date components.
• Extended time intervals & recurring intervals: rules for representing long or complex intervals and repeat rules for recurring time ranges.
• Sets and choices of dates: representations for sets (collections) and choices of calendar dates, including range expansion.
• Grouped time scale units: definition and use of grouped units (e.g., custom sub-year groupings, seasons) and rules for conversion to basic units.
• Divisions of a year: specification of seasons, decades, centuries and other sub-year groupings.
• Date/time arithmetic: standardized expressions for performing or representing simple arithmetic on date and time values.
• Time shift and UTC: representation of time shifts and offsets consistent with UTC-based time scales.
• Qualification and precision: mechanisms to qualify components (complete, group, individual) and indicate precision.
• Exclusions: does not define character encoding or non-Gregorian calendar elements.

Practical applications and who uses it

ISO 8601-2 is useful wherever precise, machine-readable extended date/time semantics are required:

• Software developers and API designers needing standardized timestamp and interval formats for data interchange (APIs, microservices).
• Database architects and data modelers who store recurring schedules, sets of dates, or uncertain/approximate historical dates.
• Archivists, historians and scientific data managers requiring representation of partially known dates and long time intervals.
• Scheduling systems, calendar apps and IoT platforms managing grouped time units, repeats and time shifts.
• Standards implementers and integrators extending ISO 8601 compliance with more expressive temporal constructs.

Related standards

• ISO 8601-1 - Core date and time representations (base rules that ISO 8601-2 extends).
• Standards for character encoding (e.g., UTF‑8) should be applied separately, as ISO 8601-2 does not address encoding.

Keywords: ISO 8601-2, date and time representations, extensions, UTC, uncertain dates, recurring intervals, grouped time units, ISO 8601 extensions.