Converging the Data Models

[Francois Bonnarel]

Dear Jonathan
Dear all;
   This is just a partial but "political" answer to part of 
Jonathan's mail.

<From owner-dm at eso.org  Thu Sep 16 19:52:52 2004
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<From: Jonathan McDowell <jcm at head.cfa.harvard.edu>
<Date: Thu, 16 Sep 2004 13:58:38 -0400 (EDT)
<To: dm at ivoa.net
<Subject: Converging the Data Models
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<
<
<A proposed simplified XML schema for Char, STC and Q.
<-----------------------------------------------------
<
<During my long silence, I've been thinking hard about how to unify the
<approaches of CDS (Characterization), Arnold (STC), and Brian et al
<(Quantity).
<
<First, some observations:
<
<  - The objects in Char are very close to the concepts elaborated in STC,
<    but Char redefines these because Francois and Mireille don't want the
<    Char definition to be dependent on the complexities of STC.
<
<  - Elements in Arnold's schema are very similar to Quantity, but
<    don't use the Quantity schema.
<
<The problem here is that each schema is so big, when done right,
<that it's hard to buy in to it. But we must reuse components rather
<than all go off in separate directions. So I have a proposal for converging us:
<
<1) The Char schema should use the appropriate STC and Q elements, but in
<an initial definition should use a relatively tiny toy STC and Q schema
<which would be  included in the Char definition. 
<
<2) Toy-STC would have the property that element instances of Toy-STC would
<   be valid instances of full STC. Same for Toy-Q. Therefore, 
<   a simple change to the namespace references would be all that is needed to
<   layer Char on the full STC and Q. The existence of the full STC and Q
<   schemas give us the guarantee that Char elements defined in this way
<   are suitably extensible in the future.
<
<3) Of course, there will be many valid instances of full STC that will
<   not be instances of Toy-STC, and so anyone using full STC underneath Char
<   might make Char instances that are not valid instances of the simple Char.
<   So, interoperable deployment of the full version would need to be
<   coordinated.
<
<I know that Francois and Mireille would prefer to just redefine the
<concepts and perhaps use choice groups to access their definitions
<versus the STC definitions. I'm not keen on this because the serializations
<are not interoperable.
<
<

------> I must correct here a little bit what is said by Jonathan.
The real point is what we think that Characterization has to allow for
several levels of quality of image description. Image Retrieval ( à la
SIAP) functionnalities can bare a coarser description (Central Position and 
bounding box) than applications which need a full description of the support
as STC AstroCoordArea. What we have in mind is more or less what was proposed
for "Coverage" in the case of Spectrum data model.

   Mireille and I will answer on the technical solutions proposed by JMC and BT
tommorrow

Regards
François


=====================================================================
Francois   Bonnarel               Observatoire Astronomique de Strasbourg
CDS (Centre de donnees          11, rue de l'Universite
astronomiques de Strasbourg)    F--67000 Strasbourg (France)

Tel: +33-(0)3 90 24 24 11       WWW: http://cdsweb.u-strasbg.fr/people/fb.html
Fax: +33-(0)3 90 24 24 25       E-mail: bonnarel at astro.u-strasbg.fr
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