Dear Laurent,
From: Laurent MICHEL <laurent.michel-at-newb6.u-strasbg.fr>
Subject: Re: adql and votable
Date: Fri, 09 Jun 2006 12:06:04 +0200
> Dear all,
>
> I'm a newcomer in the discussion and I didn't attend the side meeting
> mentioned by Gerard so I hope not to be out of the main topic.
> As wrote Gerard, JDBC or even SQL could not return semantic metadata as
> column UCDs or units because this information is domain dependant.
> This information must be stored into the database according to a
> specific schema which can not be supposed to be uniform in all datacenters.
> Any low-level solution (SQL or JDBC) to resolve this table association
> (data/metadata) will closely depend on the database implementation. So I
> don't understand how we can get this metadata just using JavaCC.
> Does it mean that some specific statement are added to the query language?
> Why not use a SkyNode interface providing UCDs and units with the Column
> webservice?
No, any specific statement will not be added to the query language.
As far as I understand, what Gerard is saying is about how to determine the unit of a derived column such as "a + b" and "a * b". So it is an issue of implementation of how to fill the field metadata of the returned votable, and not an issue of query language itself.
Yuji Shirasaki. Received on 2006-06-13Z02:52:17