Re: Normalisation

From: Paul <paul_at_test.com>
Date: Mon, 04 Jul 2005 12:56:37 +0100
Message-ID: <42c923f5$0$41924$ed2619ec@ptn-nntp-reader03.plus.net>

Jan Hidders wrote:

>> Are values in domains not atomic by definition, irrespective of any
>> internal structure they may have? (Structure invisible to the relational
>> operators, that is).

>
> Yes, but that depends a bit on what you take as "the set of relational
> operators". If that includes nesting and unnesting then you make the
> structure of nested relations visible, and you should therefore consider
> them non-atomic.

OK I see. I've never understood the appeal of "nesting" or "unnesting" relations. It doesn't seem to add anything to the relational model and only serves to complicate things. Does anyone have a concrete example of the usefulness of this? Any I've seen in the past seem to be trival to implement in a standard relational model.

I agree that there is nothing to stop someone having a "relation" domain but I think this should all be encapsulated in the domain and not pollute the relational model. Also, I question the practical sense in doing this as well. It seems a bit like having a database-valued domain and "simplifying" your database to be a single value in a one-rowed, database-valued table.

Paul. Received on Mon Jul 04 2005 - 06:56:37 CDT