Subject: Structured keywords

From: "FORVEILL@FRGAG51" <[email-masked]>
Date: Thu, 30 Nov 89 10:17:18 EDT

Date sent:  30-NOV-1989 15:51:14.09
To:   DISHFITS@NRAO
 
A few comments on the message of Bob Hanisch
 
I think we do need structured keywords soon. I agree with Bob that the need
is not urgent for transport between different reduction systems. The main
reason is that the core keywords (as defined in the original paper) are more
or less sufficient for reduced data, and that nothing else is really interpreted
in most such cases.
However, FITS is no longer used only for transport. We are porting CLASS to
Unix and intend to use FITS to convert the data between incompatible hardwares.
AIPS uses FITS to transport their internal data structures between major
versions of the data format. FITS is used to constitute archives that will
remain readable forever. Some people plan to use it as an internal format,
which makes good sense on IEEE hardware. In all these cases, one wants to
transmit more than a mere data matrix, and structured keywords are then
necessary.
If no general agreement can be reached in the short term (say within 6
monthes), we should aim for an agreement within the radio community,
where there seems to exist a consensus for some form of keyword hierarchy. If
we cannot agree, even within a limited community, we will proceed on our
own and implement the HIERARCH scheme. I am fully aware of the importance
of universaly accepted standards, but endless discussions are not acceptable
when the need is getting urgent. The consequences for non conformant readers
will be minimal: they will ignore this intrinsically private information.
AIPS has been doing that for a decade using HISTORY and nobody ever complained
about it.

        Thierry