[DALI] timestamp format

[Steve Allen]

On Thu 2013-11-07T09:29:31 -0800, Patrick Dowler hath writ:
> Not sure I follow. I agree with the goal of removing tz complexity
> from the situation I do not understand* why one would not just
> include the Z (always) and thus actually comply to the ISO8601 spec.
> To not include the Z, one cannot say this is a subset of ISO861,
> where that spec says subset (profile) means "one of the allowed
> forms, with the same meaning". What we seem to have is one of the
> allowed forms, with a different meaning. At least that's how I read
> the meaning/intent of ISO8601...

Without digging through the archives of the FITS Y2K discussions my
impression is that the idea was that the particular subset (and that
use of "subset" may not mean the same thing as terms in the ISO
document) was clear and unambiguous over the range of dates expected
to be found in digital astronomical data sets, and also that it was
dangerous to allow that there might be timezone information.

Finally, there was also the notion that the FITS standard had to be a
complete description on its own merits -- independent of other
documents and standards that might change, and so there is explicitly
no mention of ISO 8601 in the approved FITS documents.

Thus I believe we had the notion that FITS DATExxxx keywords would be
parsed by special purpose routines.  This was obviously naive and
lacking foresight of budget-constrained futures where off-the-shelf
APIs end up being used even when they contain features which are
inconsistent with the FITS standard.

Perhaps this application wants a footnote explaining that FITS
DATExxxx strings are not ISO 8601, but by adding and removing
the 'Z' when handling them they can be processed by APIs that
expect to handle ISO 8601.

--
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