RFC for UCD is ending

[Robert Hanisch]

Sorry for being so late to this discussion, but the advantage is that this
is a fresh look at the UCD1+ proposal.  Well, that is my rationale, anyway!

Minor issues:  there are a number of grammatical errors and inconsistent
usages (e.g., sometimes UCD is singular and sometimes plural; it would be
clearer, I think, to write "UCDs" when the plural is intended).

Has anyone expert in Backus-Naur Form checked Section 2.2?  There is one
mistake, I think, in that <Alpha> is defined with a capital A but the
subsequent components refer to <alpha>.  UCDs are case-insensitive, but is
BNF?

On p.7, the paragraph beginning "The order in which words are arranged..."
seems like circular reasoning to me.  It says the order matters only if the
order matters.  I think the standard should be clear on this -- does the
order matter or not?  The text elsewhere suggests yes.

I find Section 3.4 confusing...does anyone else?  phot.color is a difference
of two magnitudes, but does NOT have the associated word arith.diff.  A
temperature ratio is not a temperature, so phys.temperature;arith.ratio
seems backwards to me.  I can't use arith.ratio for M/L, so instead I see
that this is defined as phys.mass.light.  The UCD
phys.mass;phys.luminosity;arith.ratio would seem to make more sense.  If
phot.color;em.opt.B;em.opt.V means B-V and phot.color;em.opt.V;em.opt.B
means V-B, then order is clearly important.  The concern this all raises for
me is that the construction rules for new UCDs are not very clear, and that
the existing UCD1+s have a certain (large) amount of arbitrariness.

I think the list of UCD1+ words at
http://cdsweb.u-strasbg.fr/UCD/ucd1p-words.txt HAS to be included in this
document, or else we do not have a complete specification.  I understand
that the vocabulary is to be extensible.  An acceptable alternative would be
to put forward the full list of UCD1+s in a second document, but I think it
is important that this document is under IVOA auspices and that revisions
ultimately go through the same review process.  This is somewhat at odds
with Section 9, I realize.  I suspect Section 9 is written the way it is to
assure flexibility and timeliness in adding new UCDs.  Hopefully our process
is flexible and timely enough now, but if not, one could certainly entertain
"provisional" UCDs, which are deemed reasonable by the UCD Steering
Committee but remain subject to broader review.

It is great that our colleagues at CDS have set up the interface for
requesting new UCDs and is keeping the UCD lists up to date, but I think it
is really best if these services/lists migrate to the IVOA site.

In the UCD word list, why does "Q" indicate both primary and secondary
usage?

I think Section 6 should be moved to an Appendix -- it is usage advice, not
something central to the UCD1+ definition.

Cheers,
Bob

----- Original Message ----- 
From: "Sebastien Derriere" <derriere at newb6.u-strasbg.fr>
To: <interop at ivoa.net>
Cc: <ucd at ivoa.net>
Sent: Tuesday, November 23, 2004 10:23 AM
Subject: RFC for UCD is ending


>
>   Hello,
>
>   The RFC period for the UCD document is ending, and there have
> been no comments yet !!
>   If you have remarks or want changes, it is time to make them
> public.
>
> Sebastien.
>
> Sebastien Derriere wrote:
> >
> >   Dear all,
> >
> >   The UCD reference document has been uploaded to the PR area of the
> > IVOA document repository:
> >
> > http://www.ivoa.net/Documents/latest/UCD.html
> >
> >   I would like to open the 4-weeks RFC period for this document as
> > of today (Oct 27), with a close date on Nov 24, before promotion to
> > the Recommendation status.
> >
> >   A dedicated page has been created for posting comments:
> > http://www.ivoa.net/twiki/bin/view/IVOA/UnifiedContentDescriptorRFC
> >   and discussions will be conducted on the UCD mailing list
> > (ucd at ivoa.net).
> >
> > Sebastien.
>
> -- 
>     _______
>    /  ~   /, Sebastien Derriere   mailto:derriere at astro.u-strasbg.fr
>   / ~~~~ //  Observatoire de Strasbourg    Phone +33 (0) 390 242 444
>  /______//   11, rue de l'universite     Telefax +33 (0) 390 242 417
> (______(/    F-67000 Strasbourg  France
>