TAP 1.1: The table_name values must be unique

[Markus Demleitner]

Hi Brian,

On Fri, Nov 16, 2018 at 06:46:14PM +0000, Van Klaveren, Brian N. wrote:
> For TAP_SCHEMA.Tables, TAP 1.1 says:
> 
> The table_name values must be unique. The value of the table_name
> should be the string that is recommended for use in querying the
> table; it may or may not be qualified by schema and catalog name(s)
> depending on the implementation requirements.
> [...]
> Which, from a programmatic standpoint, means that an application
> must never naively qualify a table name as ( schema_name + "." +
> table_name ) when constructing a query.

That is exactly the reason for this language -- a client has a *very*
hard time to do this construction, what with different hierarchy
schemes and -- ugh -- delimited identifiers.  See, for instance,
http://mail.ivoa.net/pipermail/dal/2015-May/007116.html and
http://mail.ivoa.net/pipermail/dal/2015-May/007107.html for previous
discussions that made us introduce this kind of thing.

> I suppose that's not a dealbreaker, but I do think it's awkward,
> and it deviates from the sql99 approach of using the effective
> "catalog_name", "schema_name", and "table_name" everywhere:

Yeah, but the SQL information schema can assume a bit more knowledge
about the underlying system that we in TAP can.  Also, we couldn't
identify use cases where Ikea-style table names ("assemble yourself")
might come in handy.  Do you have one?

> I think I'd personally prefer there to be IDs and there to be joins
> on IDs rather than names in a future TAP 2.0 so joins are easier,
> but maybe at least adding schema_name columns to TAP_SCHEMA.Columns

Well, (table_name, column_name) already is a primary key in
tap_schema.columns.  So, what would schema_name in there buy you?

> approach, and just force a unique constraint on TAP_SCHEMA.Tables
> for schema_name and table_name, though I would like to see a
> CATALOG_NAME in there too.

I suppose the plan with catalog has always been to absorb it into
schema_name if you need it; no one's registered something like that
yet, though (RegTAP query:

select schema_name from rr.res_schema where schema_name like '%.%'

).  Due to the "publish ready-made table names only" rule, I'd be
fairly relaxed about that anyway.  Clients have no business mucking
with the table names, so if you have table names with five unquoted
dots, you'd still be fine (though TOPCAT's TAP client would flag
syntax errors in the editor, but that's an aesthetic defect at worst).

          Markus