[TAP] Summary: data type for column metadata

[Ray Plante]

Hi Arnold,

On Thu, 16 Apr 2009, Arnold Rots wrote:
> I am not very enthusiastic about Ray's grouping, either. I don't feel
> this level of detail needs to be in the registries and even if it is,
> it should be possible to get it from the database directly.

This is an important concern, and I agree: what's in the registry should 
not be all details obtainable from the service.  So let's state some 
scope, here.

The main use case I would like to support is a registry query that 
answers, what tables out there have XX data in them? where XX is usually a 
semantic descriptor but also may include type information.  That basically 
translates into a search against UCDs and/or UTYPEs but can also include 
type information.  For example, I'm looking for tables with RAs and Decs 
given as DOUBLEs (as opposed to formatted sexigesimal).

Some app developers have had a preference to retrieve information from the 
registry sufficient to query the service.  This in the past has encouraged 
more information.  With TAP, we'll see quite a large variation in how one 
forms queries which will be difficult to capture generically.  I think 
this is a good argument to limit the complexity of the description to the 
most common kinds of queries.

cheers,
Ray