WD-TAP-1.1 : tap_schema and VOSI-tables

[Patrick Dowler]

I have been messing around with making VOSI-tables output columns with
DALI intervals. It turns out that both TAPType and VOTableType include
an optional attribute named extendedType where one can stuff the xtype
... thus an interval could be fully described with either TAPType or
VOTableType. The same would apply to the other DALI xtypes.

However, I have to just know what dataType to use in those cases
because in tap_schema the datatype and xtype are mixed together... and
that makes it hard to write server implementation code nicely. If the
tap_schema.columns table had separate data_type and xtype columns it
would map directly to VOTable and DAI-xtypes *and* TAPType in
VODataService would be unneeded/obsolete. The whole datatype mapping
and handling would be much simpler and direct. I can't see any
downside to this aside from it being different from then ad-hoc things
we did in 1.0 :-)

* proposal *
So, although it would delay implementations somewhat, I propose that
we add an xtype column to tap_schema.columns and use the data_type
column for the underlying primitive type in TAP-1.1


Not counting case and/or prefix inconsistencies out in the wild, this
would only effect how people describe columns with the new DALI xtypes
(interval, point, circle, polygon w/ the various allowed prmtive
types). We would essentially be deprecating use of TAPType in favour
of VOTableType and extendedType but there are no xsd changes needed
for that to be valid.

Comments?

-- 
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada