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

From: sla at umbra.ucolick.org (Steve Allen)
Date: 8 Jul 1996 20:38:17 GMT

In article <4rpane$p2r at noao.edu>, Rob Seaman <seaman at noao.edu> wrote:

>Should a fundamental decision be driven by unmaintainable software?
>
>Our primary concern should be for the integrity of the FITS standard,
>and only secondarily for any particular software.
>
>- Deprecating the DATE keywords is a very large change to the standard.
>
>- Expanding the allowed formats to include DD/MM/YYYY or YYYY-MM-DD is
>  a small change.

>In any event the easiest fix is simply to add the century digits when
>writing the same old keywords, and to add an if-else clause keying off
>the length (or format) of the value when reading those keywords.

>Bill Pence's observation that a single keyword string can support
>multiple formats (distinguished by length or some other property) is
>quite provocative.  Perhaps this will prove of use with other FITS
>keywords.  A little bit of this goes a long way, of course.

To someone who feels he has already hand-crafted one too many FITS
reader/writer codes this goes a very long way.  Manually adding extra
IF/ELSE/ENDIF clauses to code is a good way to create more
unmaintainable software.  It is best to avoid such problems
altogether.  Unfortunately the only choice available which solves the
Y2K problem is whether to add the IFs to the sections of the code that
seek the keyword or to the sections of the code that parse the value.

At Lick we are toying with a FITS keyword database.  One of the goals
of this effort is the automated generation of FITS reader and writer
code.  To the extent that we have looked at this in relation to our
database we agree with Rob Seaman.  In the case of the DATE-OBS/Y2K
problem the better solution is to keep the DATE-OBS keyword and change
the syntax of its value.

This situation reminds us that FITS is a human-readable, archival
standard much moreso than it is a machine-readable, data-processing
standard.
--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 408 459 3046     FAX: +1 408 454 9863
WWW: http://www.ucolick.org/~sla                PGP public keys:  see WWW