iso-8601

<entry-title>ISO 8601</entry-title>

The International Standards Organisation's standard, number 8601 is an international standard for date and time representations. It is used for all date-time representations in microformats, as well as a number of other formats (HTML5 <time> element & datetime attribute, XML Schema Datatypes, RDF, Atom).

Image: XKCD

In addition, ISO 8601 dates in particular are the most globally unambiguously human readable/writeable date format and thus should always be used on the (world wide) web.

Overview

The following are good prose overviews of ISO 8601:

• ISO 8601 summary by Markus Kuhn
• ISO 8601 on Wikipedia

Microformats

microformats in general use a subset of ISO8601 - preferring uses which are more human readable (requiring hyphens in dates, and colons in times).

All date-time properties in microformats use ISO8601 values. E.g.

• all dt-* properties in microformats2
• all classic microformats's date-time properties, including:
  • hAtom - published, updated
  • hCalendar - dtstart, dtend
  • hCard - bday
  • hReview - dtreviewed

RFC 3339

RFC 3339 defines a profile of ISO 8601 for the use in Internet protocols and standards.

• It explicitly excludes durations and dates before the common era.
• The more complex formats like week numbers and ordinal day are not permitted (see RFC 3339, section 5.6).

ISO 8601 implementations in programming libraries

• JodaTime - the Java date-time library - ISO8601 Java calendar system
• Perl: DateTime::Format::ISO8601
• Ruby 1.9 implements an iso8601 method in the Date STDLIB but it does not handle ordinal dates.
• Glenn Jones' microformat-node parser includes isodate.js, a Node.js implementation of (some of) ISO 8601.

to do! document more implementations.

Issues

• How should dates before the common era be marked up? Andy Mabbett
  • What are the use-cases? Link to *-examples page? - Tantek
• If a web page is created or edited by a non-technical human, it is unfriendly to expect them to work in ISO date format. Charles Belov
  • ISO dates are more readable/usable by people globally than any one locale-specific format, thus it is more friendly globally to use and ask humans to edit ISO 8601 dates than asking them to try to read/write all the odd and quirky locale-specific formats. - Tantek

See also

• ISO 8601 on Wikipedia
  • ISO 8601 usage on Wikipedia
• ISO 8601:2004(E) from ISO (zip-pdf, 228KB)
• Summary of 8601 by ISO
• Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration.
• The Mathematics of the ISO 8601 Calendar
• Current date in week date and ordinal date format
• ISO 8601 at the Open Directory Project
• W3C Specification about UTC Date and Time and IETF Internet standard RFC 3339, based on ISO 8601
• StackOverflow: iso-8601 tag - questions about iso-8601 as related to JavaScript, PHP, MySQL and other programming languages and technologies.

Related pages

• datetime-design-pattern
• date-design-pattern
• abbr-design-pattern