Re: Normalisation

From: Jan Hidders <>
Date: Mon, 04 Jul 2005 18:55:30 GMT
Message-ID: <CCfye.137229$>

Paul wrote:
> 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.

Precisely. I couldn't have said it better myself.

  • Jan Hidders
Received on Mon Jul 04 2005 - 20:55:30 CEST

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