[TAP] data type for column metadata

[Patrick Dowler]

The current draft specifies that the data type is the VOTable datatype, which 
includes only primitive types and arrays of them.  However, databases also 
have timestamp/datetime columns and, with ADQL will have columns that contain 
region values. 

In the db, dates will be be timestamp or datetime (SQL type). In the output 
VOTable they will be strings  (datatype="char", arraysize="*") encoded in an 
ISO8601 format.

In the db, regions will likely be varchar or varbinary (SQL type). In the 
output VOTable they will be stringsencoded in STC/S format. 

To query a timestamp or region column, the user has to know it is one, which 
means knowing more than the VOTable datatype/arraysize. 

So, what to put in there? This effects TAP_SCHEMA, VOSI-tables, and 
VODataService.


Secondarily, should we also describe the SQL type in addition? There are some 
query writing tasks where that is needed (e.g. when implicit conversions are 
going on).

Thoughts?

-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2M7

Centre canadien de donnees astronomiques
Conseil national de recherches Canada
5071, chemin West Saanich
Victoria (C.-B.) V9E 2M7