Re: Relational Databases and Their Guts

From: Paul Vernon <paul.vernon_at_ukk.ibmm.comm>
Date: Wed, 25 Jun 2003 11:01:39 +0100
Message-ID: <bdbs2l$1l6u$1@gazette.almaden.ibm.com>

"Bob Badour" <bbadour_at_golden.net> wrote in message news:AH3Ka.442$0j4.62704888_at_mantis.golden.net...
> "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
> news:bd9ao7$13qa$1_at_gazette.almaden.ibm.com...
[snip]
> > > Now, what in your mind means logical data independence?
> >
> > Strictly I think of it as:
> >
> > The ability to interact with a database via any information equivalent
> > database schema.

> That ability is trivial. How does it provide independence? How does it allow
> one to change the base relations to a different information equivalent
> schema without requiring one to alter existing applications? Your statement
> above only requires that one can change the application to use the new
> schema, and I do not think that provides any independence at all. Or am I
> missing something?

Let me reword it as:

The ability to interact with a [subset of a] database via any one of multiple information equivalent[subset] database schemas defined to the RDBMS

"base relations" are in the eye of the beholder.

Logically, all equivalent schemas are equal, there is no requirement to make one more equal than the others by making it 'primary'. Other than each user choosing one as their current schema that is.

Physically, one schema will be picked as the basis for physical implementation. This schema can be called "base" if you wish, but users should not care.

Regards
Paul Vernon
Business Intelligence, IBM Global Services Received on Wed Jun 25 2003 - 05:01:39 CDT