STC in VOTable: Common container?

[Mark Taylor]

Markus,

On Wed, 31 Mar 2010, Markus Demleitner wrote:

> As you know, I'm currently revising the STC-in-VOTable note
> 
> (http://www.ivoa.net/cgi-bin/twiki/bin/preview/IVOA/STCInVOTable)
> 
> I'm setting out to include the feedback I've received recently -- in
> particular, there will be a "for the impatient" section that should
> cover at least 80% of the use cases with 20% of spec effort -- and to
> correct some conceptual errors that had sneaked in.

Good plan.  I have one related suggestion: can you make it explicit
in that "VOT-STC for Dummies" section or in some other prominent place
that most of what's going on here is simply specifying utype/value pairs;
with that insight it's not all that complicated, but without it it is
very easy to get lost in the forest of angle brackets.
 
> So far, I've basically maintained the basic premises of the original
> note.  Now, Arnold Rots suggests putting everything belonging to a
> specific coordinate system into one common container.  I like this idea
> very much because it would simplify implementation considerably (I say
> this as someone who has implemented the current scheme).
> 
> The downside is that the internal re-use of coordinate systems becomes
> impossible.  I personally believe this is far outweighed by the
> simplifications afforded by doing away with the separate groups, but I'm
> told other people are very fond of having ID and ref on these groups.

This proposal has my support.  Like Markus, it seems to me that the
benefits (improved comprehensibility for machines and humans) outweigh 
the disadvantages (possible loss of compactness where coordinate system
information is heavily re-used); IMO comprehensibility is at a much
higher premium here than metadata byte count.  I will add the disclaimer 
that unlike Markus I have not attempted to implement any part of any
version of STC-in-VOTable, so it is possible that there are some 
issues of detail lurking that I have not considered; I am willing to 
reconsider my opinion if anyone brings such a thing to light.

Mark

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/