updated VODataService WD Spec and Schema

[Ray Plante]

Hi RWGers and TAPers,

Following up on the discussions of the TAP metadata schema over the past 
few months, I've updated the VODataService specification and schema as 
v1.10, which are currently both available from 
http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/VODataService. 
(Submission to the IVOA Document Repository as a working draft is in 
progress.)

I'm pretty happy with the current version and would like to move to an RFC 
if there aren't any major objections.  The 2 main changes in this version:

   *  The <dataType> element for column descriptions now requires an
      xsi:type attribute to indicate which set of standard names the data
      type name drawn from. There are two sets defined: vs:TAP (containing
      the TAP data types) and vs:VOTable (containing the VOTable types
      suppported before).

      The motivation for this is:
       o  to support the recently defined TAP data types
       o  to make it straight forward to convert a service metadata query
            to a VODataService table description (e.g. in the context of a
            VOSI service), regardless if this it is a TAP service or an
            existing "Simple" DAL service.

   *  Foreign keys can optionally be described via <foreignKey> elements
      within a <table>. The vs:ForeignKey type allows one to pair up
      columns from the current table with columns in another table.

Completing VODataService can allow table metadata to be pulled via the 
VOSI service interface.  If you are involved in registries, VOSI, or TAP, 
I encourage to you to look over the relevent parts of the VODataService 
spec.

Thanks to everyone who made contributions!

cheers,
Ray