ISO8601 for dates?

Hi all,

There's an ancient issue in RDF land with modeling dates and times well. Generally, you have to "pick a lane":
* do I want just a "date" (xsd:date) with no time expression
* do I want a "date + time" (xsd:dateTime) where every date MUST come with a time
* do I want just "time" (xsd:time)

The pain shows up when you try to model/express/hold a date *and/or* time in a single field—which is not uncommon in event systems, etc.

What most "just JSON" developers seem to want (or expect they can have) is something closer to ISO8601 where there's one date(and/or time) format "to rule them all" such that a single field can hold:
* 2025-10-14 (date)
* 14:04:51Z (time)
* 2025-10-14T14:04:51Z (date and time)

The Wikipedia page for ISO8601 has some more examples: https://en.wikipedia.org/wiki/ISO_8601

I realize y'all know all of the above. ;) What I'm pondering is would JSON-LD/RDF benefit from a defined ISO8601 datatype to support these (and more)?

There is, in fact, RFC5141 <https://www.rfc-editor.org/rfc/rfc5141.html> which defines URNs for ISO specs, so in theory, this could look something like the following:
<#thing> <createdOn> "2025-10-14"^urn:iso:std:iso:8601

Obviously, choosing this datatype does push the "understanding" of what's inside to...well...what's inside, so there are still valid reasons to use the XSD datatypes which provide a clearer "look before you leap" experience. However, what this ISO8601 datatype could provide is scenarios (which are all too common...) where `xsd:dateTime`is chosen but with the full expectation by the ontologists that the time may be set to `00:00:00` and *not* mean midnight, but instead mean "ignore the time".

So, I realize this is an antique issue/topic and this may not be anything like a solution for all the problems...but I thought I'd propose it and get some feedback. :)

Thanks for entertaining this idea!
Benjamin

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