> I am afraid you have lost me here. I see no reason to infer that queryData is
> some sort of estimate on the work required to do the real thing. In SIA it is
> a query and returns the query result. It happens that the query result itself
> describes something else and one column (hopefully) contains a URL to the
> something else. It is not an estimate.
I'm no expert on this subject, but I know that producing a meaningful estimate for an arbitrary SQL query is a non-trivial task, support for which is somewhat RDBMS-dependent.
For those trying to provide generic data services that can operate as a front end for a wide range of back-end RDBMS systems, it is potentially impossible to produce an interoperable and meaningful query-estimate implementation.
Additionally, TAP might well be a useful access mechanism for "custom" tabular data services with something other than an RDBMS in the back end; in these cases there might be no estimation functionality available at all.
In other words, support for query estimation isn't necessarily universal in data services. How would the queryData/stageData metaphor work in the situation where the service (for whatever reason) does not support query estimation?
Cheers,
Kona
-- Kona Andrews kea-at-roe.ac.uk AstroGrid Project http://www.astrogrid.org IfA, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJReceived on 2007-05-02Z16:36:46