request to modify VODataService schema

[Patrick Dowler]

There are currently two xml schemas that can describe a table (eg in a
TAP service):
- VOTable
- VOSI-table (via the VODataService schema)

These are both capable of providing a consistent definition of a
table, with a few minor discrepancies. Ideally these two forms could
convey the same metadata about tables and columns.

The item that I am currently running into is the ID (type="xs:ID")
attribute on field elements, which in VOTable are used with DataLink
service descriptors in ref attributes. So, when you query a service
and get a VOTable, you find out which columns have ID attributes and
thus can be the target of a ref... it is not possible to convey that
ID in a column element in a VOSI-table description.

I think it would be completely safe to add an optional ID attribute to
the column element and make the metadata equivalent to that in the
VOTable field element. I don't foresee any other changes to make
VOSI-table and VOTable more consistent or need/desire to assign IDs to
other elements. I also do not think this needs to be an actual "xs:ID"
for ID/IDREF purposes (not usable anyway without adding "xs:IDREF"
attributes elsewhere), so it could probably be just a string.

The use case is in the context of WD-TAP-1.2 where we are extending
VOSI-tables to allow users to create tables; we support both formats
and want to enable users to assign an ID to columns/fields and we want
both formats to be equivalent.

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