Re: Proposal: 6NF

Jan Hidders wrote:
> dawn schreef:
>
> >
> > What is an accurate generalization or abstraction from Pick? What are
> > the precise features that permit this example of a function with null
> > in the range of a function within the dbms environment? I thought the
> > 2VL was a key factor in null being a value rather than a non-value as
> > it is in SQL.
>
> Close, but not exactly. In the context of database theory the most
> relavant definition of a value is:
>
> Something that can be stored in a computer and for which an equivalance
> relation is defined over its representations that defines equality.
>
> Since in SQL it does not hold that NULL = NULL the notion of equality
> is not an equivalence relation (which must be reflexive, symmetric and
> transitive) so by the above definition SQL does not treat NULL as a
> value.
>
> -- Jan Hidders

Yes, making sense as always Jan. I thought I was clear that it is outside of SQL that one can define NULL to be a value. --dawn Received on Sun Oct 08 2006 - 00:05:06 CEST