[TAP] data type for column metadata

[Doug Tody]

On Thu, 26 Mar 2009, Patrick Dowler wrote:

> * datatype: the current draft uses VOTable types but we have shown several
> places where that is not adequate and concluded that we need to use a list of
> types from ADQL/SQL

It may be preferable to distinguish at least two levels of datatype,
e.g., the VOTable type and the DBMS type (JDBC would probably be
most useful while still providing some DBMS independence; native
SQLtype is also possible).  We will have to deal with the VOTable
type in any case since this is how data is returned.  But it is
useful to know more about what is actually stored in the database.
Hence all we might have to do is add an additional bit of metadata.
Some clients might be happy with just the VOTable type.

> * system: I propose that column metadata include a place to specify the
> coordinate system applicable to values; name TBD depending on what in
> actually needs to contain

This could be useful provided we don't get carried away and make
it too complicated.  Perhaps a simple string such as TT-ICRS-TOPO,
UTC-FK5-GEO, etc., provided mainly for human consumption.  Note VOTable
has a more robust programmatic capability for assigning coordinate
systems to table columns.  But it would be useful to have something
directly in the TAP schema.

 	- Doug