Re: Functional Dependencies > Uniqueness Constraints

paul c wrote:
> Marshall wrote:
> >
> > ... (And of course there must be a rule that
> > says every base table must have at least one functional
> > dependency in which the union of the determinant set
> > and the dependent set equals the set of attributes. (This
> > restriction is sufficient to ensure every base table is a
> > relation; is it necessary?))
> > ...
>
> I would say not necessary. If a table is a representation of a
> relation, then I`d think that even if no rule is stated, by definition
> the union of the attributes is a CK, eg., if there is no stated
> determinant set, all the attributes are in the dependent set. I can`t
> think why one would want to state this, shouldn`t a dbms assume itÉ

Modulo the elsewhere-mentioned terminology issue, yes. The way I usually think of it is that the system would reject a base table declaration in which there was no key, but it is just as valid to propose that the system would create a default one containing all the attributes.

Marshall Received on Thu Aug 31 2006 - 01:21:41 CEST