[iaufwg] [fitsbits] Start of the 'INHERIT' Public Comment Period

[Steve Allen]

Note that I redirect this to IAUFWG alone in order to
reduce the distraction on FITSBITS.

On Fri 2007-04-06T15:32:49 -0400, Arnold Rots hath writ:
> That's neither here nor there for the present discussion, but I
> mention it to indicate that I feel it would be a bad idea to change
> our mind on the principle of self-sufficient HDU headers.

Within the context of FITS I don't see any alternative to spreading
important information across multiple HDUs.  The only way to encode
arbitrary amounts of structure in a FITS HDU right now is with tables.
A table which can represent arbitrary amounts of structure is almost
guaranteed not to be normalized in the sense of good database design.

It is explicit in the FITS files produced by our multi-slit
spectrograph that the slitmask design is attached using many separate
table HDUs which are the normalized subset results of SQL queries on a
normalized database.  This scheme is used from the point of submitting
the mask design, through its manufacture and use in the telescope, and
in the data reduction pipeline.  As such it is the only optical
spectrograph on Keck whose images can be reduced without the use
of data slaves manually transcribing data, and the grassroots never
stop asking why the other spectrographs don't do it.

I really wish that there were a conventional mechanism which
described the primary and foreign key relations between all of
the HDUs on these images, and which would thus serve to indicate
that they all must be handled together in a self-consistent
fashion.

Even disregarding the attached binary tables, the 8 or 16 image HDUs
have no convention for describing the reason they are all combined
into a single FITS file.  This in particular is a thorn in the side
of Bill Joye as he tries to enhance ds9 to "just know" what to do
with a FITS file that comes over a HTTP connection from far away.

I really want to describe relations, but I don't have a good enough
idea about how to do it in a simple but general way.

This is not to say that I am sure we can, or should, try to stretch
FITS to describe arbitrary relations between HDUs.  But if not FITS,
what sort of alternative will work best for the community?

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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