TAP information schema

[Doug Tody]

On Thu, 11 Oct 2007, Patrick Dowler wrote:

> Also, is either of sync or async an optional capability? My feeling is
> that at a minimum sync is required and async is optional, but anyone
> with a decent sized database is going to implement async.

Agree.  Sync, probably provided as a simple GET, should be required,
and is adequate for simple services or typical simple queries.  Async
should be an optional advanced capability since it is so complex.
However it will be required in practice for many services to do
anything complex like a multi-region query.

> Further, I think a TAP service should have the option of refusing to
> execute a query in sync mode and telling the caller that async must
> be used. We would need to specify exactly how the service makes this
> known, but in the general case a service may decide after seeing the
> query itself so I think this is a sort of result or error message
> (actually more like an http redirect) that clients will have to
> deal with.

In current DAL services this is done with an error response VOTable.
One just returns a status of OVERFLOW (or whatever code we want), and
the query fails.  The client would then have the option of using the
async option, if both the client and service support this capability,
or possibly resubmitting a simpler query.

	- Doug