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Concluded WG Serialising Extended Data About Times and Events (sedate)

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WG Name Serialising Extended Data About Times and Events
Acronym sedate
Area Applications and Real-Time Area (art)
State Concluded
Charter charter-ietf-sedate-02 Approved
Document dependencies
Additional resources GitHub Repository
Zulip Stream
Personnel Chairs Bron Gondwana, Mark McFadden
Area Director Francesca Palombini
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Closing note for Working Group

The working group has finished its chartered work.

Final Charter for Working Group

RFC 3339 defines a text format as a profile of ISO 8601 that can reliably express an instant in time, either in UTC or in a local time along with the offset against UTC. However, datetime data often has additional context, such as the timezone or calendar system that was in use when that instant was recorded.

Particularly when using times for interval, recurrence, or offset calculations, it is necessary to know the context in which the timepoint exists. It would be valuable to have a standard text serialisation format for this contextual data. This working group will develop and publish a format meeting that requirement, subject to the additional constraints described below.

  • This format must be able to round-trip through intermediate systems which do not understand the full context.

  • Systems which don’t understand all the contextual fields must still be able to reliably extract the instant in time.

This format will be a companion to RFC 3339 rather than a replacement, embedding unaltered RFC 3339 data in a way that makes it easy to parse just the datetime data independently of the context.

The work on this format discovered an issue with RFC 3339. When ISO 8601 was revised in 2000, the “-00:00” offset which RFC 3339 had invented for “offset isn’t relevant” was made invalid. This means that RFC 3339 is not a strict subset of the current version of ISO 8601.

To fix this issue, the working group will additionally update RFC 3339 by removing the definition of “-00:00” and updating the definition of “Z” (Zulu) to mean that the offset to local time is not known, leaving “+00:00” to mean that UTC is the preferred reference point for local time.

Any other changes to RFC 3339 are explicitly outside the charter for this working group. If a need for any other changes to RFC 3339 emerges, this group must recharter before performing that work. In this case, the changes to RFC 3339 will need to be clearly motivated, evaluated and precisely scoped during the rechartering process, and will need to make only changes that keep the timestamp specification a profile of current versions of ISO 8601. Stability of the RFC 3339 timestamp format is important to existing IETF protocols and the Internet generally, and any rechartering process should frown on anything that would invalidate the existing timestamp format.

The working group will coordinate with ECMA International TC39 and ISO/TC 154 to ensure that this work remains a strict extension of ISO 8601 and its various parts rather than becoming a conflicting standard.


Date Milestone Associated documents
Apr 2023 Submit extended date and time draft to the IESG for publication draft-ietf-sedate-datetime-extended