Subject: Re: DATE-OBS='31/12/99'

From: Preben Grosbol <pgrosbol at eso.org>
Date: Fri, 28 Jun 1996 14:23:11 +0200

Rob Seaman writes:

>Whatever solution is adopted should be graceful, not just functional.
>If functionality were the final word, I would instead advocate a
>variation on DD/MM/YYYY:
>
>    DATE-OBS= '24/06/96/19       '
>
>This would undoubtedly break less current software and offers precisely
>the same information, but aesthetically it's indefensible.  Not "breaking"
>software is also not the same as not requiring software to change - the
>millennium would still leave us with DATE-OBS='01/01/00/20' to deal with.

 It is very important not to fool old FITS readers.  Thus, the first
8 characters of data value strings for 'DATExxxx' keywords must be
maintained as 'dd/mm/yy'.  I agree with Rob that the double keyword
solutions e.g. 'CENTxxxx' have a number of disadvantages.  Also a whole
set of new e.g. ISO8601 formated data keywords may be too much.
Although it may not be so 'graceful' Rob's proposal to add additional
charaters may be the less harmfull.  To make it a little more
readable I would rather suggest something like:

    DATA-OBS= '24/12/01:2001'

It is redundant but more readable.  It would make it reasonable
easy to specify a backward compatible rule e.g. 'Date value strings
which have 8 character or have no ':' as their 9th character specify
a date in the 20th century (i.e. 19yy).  If the 9th character is ':',
the full year follows as an integer.'

Preben Grosbol