Re: 1 NF

On Mar 2, 1:54 pm, "JOG" <j..._at_cs.nott.ac.uk> wrote:
> On Mar 2, 10:40 am, Stefan Nobis <sno..._at_gmx.de> wrote:
>
> > Gene Wirchenko <g..._at_ocis.net> writes:
> > > "Alfredo Novoa" <alfred..._at_gmail.com> wrote:
> > >>1NF is irrelevant because any relation is in 1NF by definition.
> > > It is relevant for precisely that reason. It sets a
> > > precondition.
>
> > No. The term "relation" is defined without any mentioning of 1NF. So
> > 1NF is not a precondition.
>
> This response is a non-sequitur I think Stefan. A relation does not
> have to be defined using the term 1NF for it to /be/ in 1NF.I believe
> Alfredo was stating that using relations as a precondition for your
> modellling, meant that your data would be inevitably be in 1NF, which
> is spot on.
>
>
>
> > --
> > Stefan.
>
> My perspective is not that 1NF => relations. Rather the opoosite -
> that using relations to model propositions enforces 1NF (i.e. I see no
> reason another data model could be in 1NF even if it did not use
> relations):
>
> * Using a mathematical relation means that all the propositions
> collected in that set have to have the exact same structure.
> * A relation definition forces each element of a tuple to be /one/
> value taken from that attributes associated domain.
> * Hence using a relation prohibits an element simultaneously
> containing multiple values from the associated domain.
> * This is what I believe Codd intended when he used the term 'atomic
> value' (I think there were probably less-ambiguous terms he could have
> used - "single value" perhaps).
>
> N.B. That if the domain is {1, 2, 3, 4, 5} the value "{1, 2}" is not
> in this domain . This is why an MV approach /using sets/ makes no
> sense to myself.
>
> I have swung wildly in my understanding of 1NF and whether or not it
> made sense to me. I've come out the other side with the belief that
> 1NF is absolutely essential for good data modelling. However I also
> believe that being in 1NF does not necessarily preclude propositions
> with multiple-values (you just couldn't use relations to store them).
>
> It is very hard to debate this though because many often assume that
> 1NF => relations and MV => NFNF, both of which are wrong. Rather
> relations => 1NF and NFNF => MV.
>
> Regards, J.

<<* This is what I believe Codd intended when he used the term 'atomic value' (I think there were probably less-ambiguous terms he could have used - "single value" perhaps).>>
Nice to notice. Another way to ask the question: What are the chances for a logical schema to be in 1NF if at least *one* or more of the logical entities that constitutes it, do not reflect a 2VL validated *relations*. Answer: None.

Next Question: how does one validate a 2VL logical proposition to TRUE with one of its argument being a physical argument... Received on Fri Mar 02 2007 - 14:10:16 CET