[TAP] Summary: data type for column metadata

[Ray Plante]

Hi type enthusiasts,

Thanks, Pat, for the summary and calling for questions.  My interest, of 
course, is in adapting VODataService accordingly.

On Wed, 15 Apr 2009, Patrick Dowler wrote:
> 1. use ADQL datatypes rather than VOTable datatypes:
>
> BOOLEAN, SMALLINT, INTEGER, BIGINT,
> REAL, DOUBLE,
> TIMESTAMP,
> VARCHAR, VARBINARY,
> POINT, REGION

I like this list.  I think we also need to include a recommendation (at 
least) for how these should be mapped to VOTable types.  This is not only 
for consistency in TAP responses, but also for describing a table 
in the registry outside the context of TAP (e.g. describing the table
returned from an SIA query).  Does this seem reasonable?
    ADQL type      VOTable
    BOOLEAN        boolean
    SMALLINT       short
    REAL           float
    DOUBLE         double
    TIMESTAMP      char arraysize="*", (format?)
                    (or is it numeric?)
    VARCHAR        char arraysize="*"
    VARBINARY      char arraysize="*", format not specified
    POINT          char arraysize="*", STC/s format
    REGION         char arraysize="*", STC/s format

We could get away with making this mapping only a recommendation if the 
SCHEMA and/or VODataService description indicated the mapping.

> 2. add single additional optional metadata coordinate system spec

I like the idea of relying on the existing solution available in VOTable 
using GROUPs and ucds/utypes.  Of course, it would be good to capture this 
in the registry description via VODataService.  May I propose adapting the 
GROUPs model into VODataService.  Flatter structures makes searching 
easier so it probably would look exactly like it.

I sense some consensus on these two questions so far.  I would like to 
immediately turn this around into a VODataService proposal.  May I enlist 
the respondants to Pat's summary for consultation on this proposal?  (So 
far, this has been Pat, Gerard, Markus, and Mark.)

cheers,
Ray