On Fri, 16 Jan 2004, Jim Gray wrote:
> The registry will not know everything (as you postulate) about
> everyone, it will only know what it is told.
Of course; when I said "omniscient" I meant it purely in the VO context. It won't have my fingerprints, for example, (at least unless I visit the US with a passport issued after 2004 October 26, and there's some leakage of information out of some government's computers :-).
The AstroGrid model does require any registry which is accessed by the user's chosen Portal to have, or be able to get hold of, all the necessary metadata about each table (units, UCD, etc) in the VO. Furthermore the translation from user query to SQL then takes place in at least three places:
(1) from user language to ADQL in the Portal where, for example, physical units get converted,
(2) from ADQL to JDBC/ODBC in the data access layer at the data center, where
(3) from JDBC/ODBC to SQL inside the DBMS wrapper as usual.
ADQL and SkyQL are then strictly just specifications for the transport layer, neither created directly by the user, nor used directly by the DBMS. That isn't stated explicitly in the document, and maybe it should be.
I _think_ this model is a good one, and it does seem similar to that used at JHU for SkyServer etc. (if I understand things correctly), but not everyone seems to realise the implications for the design of the registry and the pivotal role it will play.
-- Clive Page Dept of Physics & Astronomy, University of Leicester, Tel +44 116 252 3551 Leicester, LE1 7RH, U.K. Fax +44 116 252 3311Received on 2004-01-16Z16:26:15