describing TAP capabilities

[Ray Plante]

TAP-ers,

As Tom underlined in his presentation on implementing TAP 
(http://www.ivoa.net/internal/IVOA/InterOpNov2009DAL/TAPImplementationIssues.pdf, 
slide 9), "TAP implementations have many choices"; consequently, 
communicating these choices is actually quite critical.  Thus, once the 
TAP document is revised and approved, defining a Capabilities extension 
schema for TAP should be popped up to a high priority.

Doug and I were talking about this, and based on that discussion, I can 
recommend a roadmap for doing this.  It is composed of 3 phases:

   1.  Incorporate my recommended changes to the TAP document regarding
       what is returned by the getCapabilities operation.  The key thing
       is setting the capability's standardID.  (This phase is essentially
       done.)

   2.  Create a simple extension that includes the most important metadata
       needed today.  We create this simply and soon and keep it
       uncontroversial.  It is *not* necessary to put this through the
       standardization process in order for the registry to start using it.

   3.  Work out the real extension schema with the accompanying document
       that covers all of the metadata that is needed.  This version would
       go through standardization process.

cheers,
Ray