UCDS vs DM - Peacekeeping

[Sebastien Derriere]

martin hill wrote:
> 
> It strikes me that data models are about structure, and UCDs about describing
> elements in that structure.
> 
> Now it is probably possible that the way data models are defined could include
> naming elements to define what they mean.  I suggest that these should be (or
> include as attributes) UCDs, at the very least so that we can compare data
> items that have been formally modelled with those that haven't.

  This kind of work has been done in the case of the IDHA model:
trying to find a relevant UCD for the different model elements.
But I don't think that we should impose every element of every 
data model to be associated to a UCD.
  In fact, the link between UCD and DM can exist in both directions:
- there can be a 'ucd' attribute for elements of data model, to
   indicate the corresponding UCD
- the 'utype' attribute in VOTable allows to give a link to some
   data model element

  In the first approach, people building the data model make the
effort to associate UCD to their view.
  The second approach can be used when there are no ucd attribute 
in the DM, to link the description of a dataset to a DM.

  Of course, both are not exclusive: there can be a ucd attribute
in the DM, AND a utype for a <FIELD> or <PARAMETER> that would
point, hopefully, to the same element of the DM !

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