Re: Normalisation
From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Mon, 04 Jul 2005 18:55:30 GMT
Message-ID: <CCfye.137229$VX3.7329860_at_phobos.telenet-ops.be>
>
> OK I see. I've never understood the appeal of "nesting" or "unnesting"
> relations. It doesn't seem to add anything to the relational model and
> only serves to complicate things. Does anyone have a concrete example of
> the usefulness of this? Any I've seen in the past seem to be trival to
> implement in a standard relational model.
>
> I agree that there is nothing to stop someone having a "relation" domain
> but I think this should all be encapsulated in the domain and not
> pollute the relational model. Also, I question the practical sense in
> doing this as well. It seems a bit like having a database-valued domain
> and "simplifying" your database to be a single value in a one-rowed,
> database-valued table.
Date: Mon, 04 Jul 2005 18:55:30 GMT
Message-ID: <CCfye.137229$VX3.7329860_at_phobos.telenet-ops.be>
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