Subject: Re: ODL and ASN.1

From: leb at Hypatia.gsfc.nasa.gov (Lee E. Brotzman)
Date: 1 Jul 92 14:37:29 GMT

Both Bill Thompson and Chris Flatters are correct in their assessment of ODL
and ASN.1, and I'm not suggesting that they be used to completely replace FITS
(at least not yet, anyway).  I just want the FITS people to know that there are
other, richer, data description languages out there.

I also posted my original letter to the WGAS mailing list, and I think that
I'll pursue further discussion over there.  The astronomical community may find
that it has a use for other commonly used data transfer formats -- heretical
as that thought may be.

By the way, I'll be starting up a newsgroup to accompany the WGAS mail exploder
called alt.sci.astro.wgas as soon as I can get the attention of the Goddard
newsfeed lords long enough to set up the two-way link to the mail exploder.
If you don't get the alt. news hierarchy, you can subscribe to the WGAS mail
exploder by sending E-mail to listserv at hypatia.gsfc.nasa.gov.  In the body of
the mail message (not the subject line) put the command:

	SUBSCRIBE WGAS Your Name

where "Your Name" is your name, not your E-mail address.  LISTSERV will get the
mailing address from the mail headers.

--
-- Lee E. Brotzman                    Internet:  leb at hypatia.gsfc.nasa.gov
-- Hughes STX                         DECNET:    NDADSA::BROTZMAN
-- National Space Science Data Center BITNET:    ZMLEB at SCFMVS
-- NASA Goddard Space Flight Center

---

From: dwells at azalea.cx.nrao.edu (Don Wells)
Date: Thu, 2 Jul 1992 17:23:33 GMT

In article <leb.710001449 at Hypatia> leb at Hypatia.gsfc.nasa.gov (Lee E.
Brotzman) writes:

 LEB> ... I'm not suggesting that [ODL and ASN.1] be used to
 LEB> completely replace FITS (at least not yet, anyway).  I just want
 LEB> the FITS people to know that there are other, richer, data
 LEB> description languages out there.. The astronomical community may
 LEB> find that it has a use for other commonly used data transfer
 LEB> formats.." 

ODL and ASN.1 are fine ideas, but they are not necessarily superior to
the current FITS agreements for the purposes of interchange and
archiving of astronomical datasets. The BINTABLE format (descriptive
language) is strong enough to describe most object types currently
used in astronomy, and the cases which it does not explicitly support
can be implemented by conventions layered on top of BINTABLE (I am not
aware of any interesting exceptions to this assertion). In particular,
the vector fields (blobs) will permit encapsulation of other objects
(BINTABLEs inside BINTABLEs) and the character fields can be used to
"point" to other BINTABLEs (trees of sets of objects). The proposed
Appendix-B pointer convention will support variable-sized objects. The
ODL and ASN.1 notations for describing objects are much more terse
than the equivalent FITS notations, but terseness of description has
never been the primary design objective in FITS negotiations. Our goal
has always been to produce archival-quality self-describing
(paperless) datasets for interchange and archiving. An important
property of our architecture is that it does not depend on an
(ephemeral?) central registry of object descriptions.

There are indeed interchange formats which solve problems for which
FITS does not currently have good solutions. The GIS [Geographic
Information Systems] community has developed a format used by USGS and
others to digitize the information carried in maps. At present I do
not believe that astronomy has applications of this type, but if it
did I would advocate that the FITS community simply declare
XTENSION='<protocol name>' to encapsulate the bitstream of the GIS
standard inside FITS files. In a similar fashion I believe that there
may be a good argument for agreeing to use XTENSION='TIFF' to attach
quick-look overview renderings of FITS objects to the files containing
those objects.

--

Donald C. Wells             Associate Scientist        dwells at nrao.edu
National Radio Astronomy Observatory                   +1-804-296-0277
520 Edgemont Road                                 Fax= +1-804-296-0278
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