Re: boolean datatype ... wtf?

On 1 okt, 19:54, Brian <br..._at_selzer-software.com> wrote:
>
> > Erwin wrote:
>
> > > Explain "cyclical referential constraint".
>
> > > And explain "additional attribute".
>
> The functional dependency AB -> CD is lost.  If that dependency were
> invalid in the 5NF schema, {A,B,C,D} KEY {A,B}, then it would not be
> in 5NF because that dependency is implied by the key, so the correct
> 5NF schema would be,
>
> {A,B,C} KEY {A,B}, {A,B,D} KEY {A,B},
>
> which just happens to also be in 6NF.
>
> In order for the functional dependency AB -> CD to be preserved, a
> cyclical inclusion dependency
>
> {A,B,C}[A,B] = {A,B,D}[A,B]

If you care to explain, my question amounted to "why do you qualify this as 'cyclical' ?".

And you also spoke of "additional attribute". Please point out to me where this "additional attribute" is in your very own answer ... Received on Fri Oct 01 2010 - 20:26:27 CEST