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ISO 8601

ISO 8601

ISO 8601 describes an internationally accepted way to represent dates and times using numbers. It was issued by the International Organization for Standardization (ISO) and was first published in 1988. The purpose of this standard is to provide an unambiguous and well-defined method of representing dates and times, so as to avoid misinterpretation of numeric representations of dates and times, particularly when data are transferred between countries with different conventions for writing numeric dates and times. When dates are represented with numbers they can be interpreted in different ways. For example the date of writing of this glossary entry, 05/07/16 could mean May 7, 2016, or July 5, 2016. On an individual level this uncertainty can be very frustrating, in a business context it can be very expensive. Organizing meetings and deliveries, writing contracts and buying airplane tickets can be very difficult when the date is unclear. ISO 8601 tackles this uncertainty by setting out an internationally agreed way to represent dates: YYYY-MM-DD. For example, May 7, 2016, is represented as 2016-05-07.

The Library of Congress has initiated a draft date-time standard known as Extended Date/Time Format (EDTF) with the intention of creating more explicit date formatting and addressing date types that are not currently regulated by ISO 8601. The EDTF is formalized as an ISO 8601 amendment or as an extension to other Web-based date standards. EDTF format is used in the MARC 21 filed 046 in the Name Authority Records in cataloging in Resource Description and Access (RDA). The current LC-PCC best practice suggests, "When supplying dates in field 046, use the Extended Date Time Format (EDTF) schema in all cases except for centuries."


  • Date and Time Format

  1. International Organization for Standardization. Date and time format - ISO 8601. (accessed 2018-07-29)

  • Last Updated: 2019-07-04
  • Written: 2016-05-07

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