What is ISO 8601-2 about?
ISO 8601-2 is the second part of the ISO 8601 series of standards that applies to extensions for the representation of the Gregorian calendar. ISO 8601-2 details basic rules for the prevention of misunderstanding the date and time format representations for information interchange. ISO 8601-2 specifies representations of dates of the Gregorian calendar and times based on the 24-hour clock, as well as composite elements of them, as character strings for use in information interchange. It is also applicable for representing times and time shifts based on Coordinated Universal Time (UTC).
These extensions include:
- uncertain or approximate dates, or dates with portions unspecified;
- extended time intervals;
- divisions of a year;
- sets and choices of calendar dates;
- grouped time scale units;
- repeat rules for recurring time intervals; and
- date and time arithmetic.
Note1: ISO 8601-2 excludes the representation of data elements from non-Gregorian calendars or times not from the 24-hour clock.
Note2: ISO 8601-2 does not address character encoding of representations specified in this document.
Who is ISO 8601-2 for?
ISO 8601-2 on information interchange is useful for:
- Historians
Why should you use ISO 8601-2?
The Gregorian calendar provides a time scale consisting of a series of contiguous calendar years, each identified by a year number represented by an integer, greater than that of the immediately preceding calendar year by 1. ISO 8601-2 is to provide a set of date and time format representations for information interchange beyond those supported by ISO 8601‑1.
There are various concepts and representations that many applications find useful not supported by ISO 8601‑2, including:
- negative values for time scale components
- qualification of expressions and time scale components
- set representation of date and time expressions
- seasons
- time intervals with open or unknown starts or ends
- expression of movable days through date and time selection
- date and time expressions without digit length limits
- profiles for specifying feature support amongst ISO 8601 (all parts) features
Such concepts are often represented according to various ad‑hoc conventions; ISO 8601-2 aims to provide a standard syntax for their representation. The extended representations allow unambiguous interpretation, enforce the confidence of interoperability and minimize the risk of misinterpretations and their consequences.