MyUCDs & Registry

[Ray Plante]

Hi Gretchen,

On Mon, 19 May 2003, Gretchen Greene wrote:
> If the registry is going to supply 'Subject' , i.e. keywords for
> targeting specific astronomical topics, then I think it would equally
> serve to provide the UCDs and their associated tags (units, type, etc.)
> for refining queries.  
> 
> Not to sound harsh,  my only question is why do we have to consider
> generating more schema files to do this?  UCD's are fundamental
> descriptors in my mind and could be included in the base terms as
> optional elements.  I guess the discretion comes from service providers
> with column descriptions not mapped into UCD's?

There is precedence for integrating it into the generic resource metadata:  
the current VOResource contains Coverage.  However, it was pointed out
last week that it is unclear, for example, what Coverage means when it
applies to an organization.  It was suggested (and I plan to look at this)
that Coverage only be associated with descriptions of Data Collections and
Services.

I mention this because it illustrates a basic modeling issue.  When UCDs
are associated with a description of an SIA service, it can be made clear
what the role the UCDs play in the service (i.e. these are the UCDs
associated with the columns returned from an image query).  Similarly, the
connection is clear when made part of a Catalog description.  However, if
they are associated with a generic resource, their role is ambiguous.  
That is, what does it mean to search for Organizations based on UCDs?

> my only question is why do we have to consider
> generating more schema files to do this?  

Your question suggests that dealing with multiple schema files has 
additional overhead costs associated with it (as opposed to just have one 
schema).  Do you see this as a problem?

We put the metadata that is not purely generic Resource metadata into a
separate schema because it makes for a friendlier extension mechanism.  
If we add new metadata that, say, specifically describes Catalogs into the
VOResource schema, it affects all users of this schema regardless of
whether they care about Catalogs.  (They may have to change their software
to cope with the new version.)  However, if we put the metadata into its
own schema that extends VOResource, it only affects those that want to
describe Catalogs.

cheers,
Ray