Re: Joining data tables and system tables

"Paul" <pbrazier_at_cosmos-uk.co.uk> wrote in message news:51d64140.0301060701.2bc73ad8_at_posting.google.com...
> mikharakiri_at_yahoo.com (Mikito Harakiri) wrote in message
news:<bdf69bdf.0301041032.4164ad44_at_posting.google.com>...
>
> > Catalog table TABLES contain relations as tuples. There is no
> > self-referential problem here.
>
> This is another interesting thing: the "table" attribute of the
> catalog table isn't relation-valued, but rather contains strings that
> "point" to the actual relation. I've just been reading Date & Darwen's
> "Third Manifesto" and according to this, pointers are a definite no-no
> in a relational database.
> Are the tables names in the system catalog really pointers?

No they are just names.

> I'm
> wondering if it doesn't matter because the the DBMS itself doesn't
> follow the pointers but leaves it up to the database user to do it
> manually. I guess also this (manual following of pointers) is the
> reason why my original query isn't possible.
>
> Paul.

Your original query is possible assuming the database user knows the names of every relation in the database. I agree that this is not always a reasonable assumption and so some method should be provided to directly perform the kind of query you mentioned. The only issue, I belive, is on the concensous on what the best method(s) would be. I can think of a few options...

Regards
Paul Vernon
Business Intelligence, IBM Global Services Received on Mon Jan 06 2003 - 20:01:51 CET