handling metadata with multiple values

[Ray Plante]

Hi everybody,

I'm happy to see all this discussion about handling multiple values.  It 
won't be the most difficult issue we will have to tackle, but I think it's 
really good to get this experience out there to inform our general 
practice.  

I'm especially happy to hear people bring up issues of meaning, as this is 
an important issue in my mind.  If we take care to define our schemas with 
meaning in mind, there will be many benefits, including a metadata 
dictionary that falls right out.  Here's an example:

  My prototype schema for resources, VOResource...
  http://www.ivoa.net/internal/IVOA/IVOARegWp03/VOResource.xsd

  ...A metadata dictionary created from this schema...
  http://www.ivoa.net/internal/IVOA/IVOARegWp03/VOResource.html

  ...using this general stylesheet.
  http://www.ivoa.net/internal/IVOA/IVOARegWp03/dictionary.xsl

One of the things that makes this work logically is that every element 
defined represents a metadata concept.  My hypothesis is that if that if 
we take care in preserving meaning, the schemas will be both easier to use 
and more widely applicable and reusable. 

Patrick's argument against the particular type of container,
<ucdList><item>...</item></ucdList>, is a strongest example of this the
importance of preserving meaning. In general though, list container
elements add very little, if any, new meaning to the schema; that is,
they're redundant in this respect.  (This is perhaps a more philosophical
take on Tom's point about needlessly doubling the size of our data
dictionary.)  Nevertheless, I see this prototyping period as a test for
these ideas.

My observation from both my experience and this discussion is that having 
a list container element (e.g. <ucdList>) does not make access any easier; 
in some cases, though, it is arguably no harder.  Nevertheless, I'm still 
interested in examples to the contrary.  If my assertion is correct, then 
the advantage of a list element is solely in how it looks.  

cheers,
Ray