Subject: Deprecation of Random Groups

From: sla at ucolick.borg (Steve Allen)
Date: 28 Apr 1998 10:08:35 -0700

Bill Cotton and Tim Pearson object to deprecation.  The text states
only that "its use for future applications has been deprecated".  This
says nothing against its use for existing applications.  Indeed, the
mere existence of section 7 appears to be acknowledgement that random
groups will always be acceptable as FITS.

Would another term with definition "should not be applied to any new
applications" be more acceptable?

-- 
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.borg     Voice: +1 408 459 3046     FAX (don't): +1 408 454 9863
WWW: http://www.ucolick.borg/~sla               PGP public keys:  see WWW
Junk mail is irrelevant -- my return address has been assimilated.

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From: Stephen Walton <swalton at galileo.csun.edu>
Date: Wed, 29 Apr 1998 09:05:55 -0700 (PDT)

With regard to the draft standard's statement that random groups are

> applications" be more acceptable?

As someone with no vested interest:  I believe that, in context, "deprecated"
means that new code which can read the old files can be written, but that new
applications should not _write_ random groups.  In the same way, several
classic Fortran-77 constructs are "deprecated" in the Fortran-90 standard. 
This means that some future standard will delete them, and that a code which
uses these constructs is not standards-conforming (and thus, potentially, the
interpretation of such code is dependent on the compiler).  Clearly AIPS 2050
will still be able to read random groups :-) .

--
Stephen Walton, Professor of Physics and Astronomy,
California State University, Northridge
stephen.walton at csun.edu

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From: Lucio Chiappetti <lucio at ifctr.mi.cnr.it>
Date: Wed, 29 Apr 1998 18:31:06 +0200 (MET DST)

> > applications" be more acceptable?

  Probably yes, specially if handled as a "recommendation".

> As someone with no vested interest:  I believe that, in context, "deprecated"
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  Me too. I never used random groups nor ascii tables.
  I will never plan to use the former in X-ray astronomy (and I understood
  they were going to be replaced by binary tables in radioastronomy, but I
  have just learned that was not the case) and I believe the latter can
  also be replaced in a more compact form by binary tables (at least that is
  what I will use for any tabular material).
  
> applications should not _write_ random groups.  In the same way, several

  One could perhaps state "outside of specific discipline fields where 
  actively used" ?

> This means that some future standard will delete them, and that a code which

  That's a different story.
  I do not regard the "deprecations" in f77->f90 as always fortunate, and
  anyhow the "once FITS forever FITS" principle does not allow cancellation.

  (Of course if one is writing a SPECIFIC reader, and not a GENERAL PURPOSE
  reader, one can always assume to be more restrictive and RECOGNISE some
  extension and just say "I do not support them")

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From: Tim Pearson <tjp at astro.caltech.edu>
Date: Wed, 29 Apr 1998 10:54:31 -0700 (PDT)

>From the proposed standard (Section 7): "The binary table extension
... can accommodate the structure described by random groups."  I
think that the binary table extension can also accommodate the
structure described by the Primary Data Array, but we have not
"deprecated" that.

Software exists to read and write data in the random groups structure
(e.g., cfitsio), so why not let application designers decide for
themselves whether the random groups structure or a binary table is
more appropriate?  Putting data in a binary table format does not make
it immediately accessible - applications still have to be written that
understand the physical or astronomical meanings of the various
columns. This is presumably why the binary table format has not
replaced random groups in radio interferometry.

I would welcome more discussion of the relative merits of random
groups and binary tables. The only advantage of a binary table that I
can see is that generic software can - in some degreee - display,
edit, or restructure the table, but this does not particularly help in
designing a real application that needs to know the meanings assigned
to the rows and columns of the table.

Perhaps everybody would be happy with a slight change of wording, such
as: "The binary table extension can accommodate the structure
described by random groups, and offers advantages over the random
groups format, so it is recommended for new applications," rather than
"its [random groups format's] use for future applications has been
deprecated", with the implication (Section 3) that a "deprecated"
structure is "obsolete".

- Tim Pearson

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From: Bill Cotton <bcotton at nrao.edu>
Date: Thu, 30 Apr 1998 07:31:07 -0400 (EDT)

I'd like to support Tim Pearson's proposed solution to the

> deprecated", with the implication (Section 3) that a "deprecated"

   While it's true that Random Groups are in a sense a subset of
binary tables with a different header and are therefore redundant,
it's also true that Random Groups have a long history, as long as FITS
images, and are deeply entrenched in the radio interferometry
community.  As Tim points out, a FITS reader is merely a front end to
a program that understands the contents of the file.  Having a more
widely understood format (e.g. binary tables) is of little use if the
underlaying software is unable to make sensible use of the
information. Specialized software will always be necessary for
complicated data such as interferometer visibility measurements.
Software issues have gotten so politicized in recent years that the
additional burden of needing "obsolete" data formats is an undesirable
complication.  

   As an amusing historical note, binary tables were invented for the
purpose of attaching calibration data to Random Groups files.

-Bill Cotton

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From: hodge at bowline.stsci.edu (Phil Hodge)
Date: 30 Apr 1998 16:30:42 GMT

To say that random groups are "deprecated" is a value judgement,
and I agree with Bill Cotton that this is not appropriate for a
format that is in widespread use.

The IMAGE extension is another viable alternative to random groups,
isn't it?

					Phil Hodge