STC and characterization

[Francois Bonnarel]

Dear Doug,
About your mail of last Saturday.
I  think there is a misunderstanding there about what I was
trying to do as an anser to Joanthan's sollicitation abot this
proprty first schema.

   a ) It was always in the intentions of the Charac Sub-group to
allow both Axis Fisrt and Property first approach.
       The UML diagram allow both.

   b ) It is true that the AxisFirst XML serialization was developped
first.

   c ) there have been people in the subgroup (Alberto, Jonathan)
pushing the other approach. It is true that it can be really usefull
when the axes areintertwinned for example.

   d ) So what we have here is an attempt to build a Property first
XML serialization. This doen't mean we want to give up the other one.
We have to propose both. and SSA can defintly rely on the Axis-first
approach.

   e ) A full Property first schema and utypes will be proposed rather 
soon on this list.


   f )  about STC and Charac. the relationships between both is 
discussed since a very long time. I think that it is mostly a
matter of xml integration and not of the models in themselves.
In the property first  option we had something rather feasible since
a long time although a way to transform from one to the other is
still missing (I am working on an xquery on char to build a full
STC structure). Apparently Joantahn thought the integration will
be more complete using the property first approach, which I think
is not completly the case? that's the on-going debate
   In any case this doesn't affect  the relationships between Charac
and DAL query responses at all.

Cheers
François






<From owner-dm at eso.org  Sat May 27 06:13:16 2006
<
<Hi All -
<
<This property-first alternative seems counter to the whole concept of
<Axis-based characterization in the current model.  Agreed, the
<Axis-based approach is counter to what we were originally doing
<elsewhere (e.g., the most recent version of characterization in
<the SSA query response), and I was at first surprised to see this,
<but it seems reasonable if we want the flexibility to allow new
<characterization axes can be added.  For example if we want to add
<a new axis to characterize the spatial frequency axis for radio data
<this can be easily done with the current model.
<
<I support use of STC to define reference frames in characterization
<and elsewhere in VO, and probably for some things like region
<descriptors, which STC is well able to deal with and which are not
<currently addressed elsewhere, but not necessarily for something as
<simple as a coordinate instance - there are many alternative ways
<to represent something that simple.  Why can't a simple coordinate
<instance in whatever representation be associated with an STC-defined
<reference frame?  In the case of characterization I am really bothered
<by the suggestion of seemingly opaque references into bits of STC for
<something for which we currently have a simple, direct, parameterized
<representation which is defined independently of implementation.
<
<This issue of overlap between STC and Characterization should have
<been addressed long ago if we are going to address it at all.
<At the moment we are on the third or so iteration of something
<which is largely compatible with what the DAL interfaces require,
<and are overdue to complete SSA 1.0, having only recently spent weeks
<discussing the issues of generic Axis descriptors among other things,
<and completely refactoring the model with all that entails is probably
<not a viable option.
<
< 	- Doug
<
<

=====================================================================
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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