DALI 1.1 comments

[Paul Harrison]

On 2016-05 -10, at 21:10, Arnold Rots <arots at cfa.harvard.edu<mailto:arots at cfa.harvard.edu>> wrote:

I don't have the text of ISO-8601 handy here, but my recollection
was that it is silent on what a time stamp without explicit time zone
information means.

I do not have a copy of the text of ISO-8601 either, but many authoritative sources make this interpretation clear e.g. https://www.cl.cam.ac.uk/~mgk25/iso-time.html#zone , https://en.wikipedia.org/wiki/ISO_8601#Times and that is how java https://docs.oracle.com/javase/8/docs/api/java/time/package-summary.html interprets strings for instance and http://tools.ietf.org/html/rfc3339 recommends UTC but adds the Z to be explicit.

There are a wide range of existing software systems (e.g. language libraries, databases) that use the strict interpretation of ISO-8601 which mean that the timestamp without will be interpreted incorrectly unless the system timezone is set to UTC, and while I can imagine that many astronomical servers around the world do have their timezones set to UTC, I doubt that all astronomers laptops are similarly set with their timezone to UTC.

Be that as it may, it does not explicitly allow for attaching time scale
labels to the date-time strings and hence pairing a bare string with
a time scale is a reasonable thing to do.
Pure use of JD or MJD is problematic if UTC is an allowed time
scale, since their values are ill-defined during days with leap seconds.
Besides, the date-time strings are nicely human readable.

This issue is why I made the suggestion earlier in this thread that only ISO 8601 be used only for the case of UTC timescale and be forbidden for other timescales - then the Z serves the double purpose of being a designator of UTC timezone and time scale whilst keeping compatibility with non-astronomical ISO 8601 usage.

Cheers,
Paul.


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