Re: Pseudo transitivity

Phil Cook wrote:

> I am told that if X ---> Y and YW ---> Z, then XW ---> Z
>
> Given schema(R) = {C,T,H,R,S,G}, I have the following FDs:
>
> HS ---> R
> HR ---> C
>
> Can I therefore say that HHS ---> C and from that HS ---> C?

You're dealing with sets of columns, so you can't write HHS -- there are no duplicates in sets.

So, HS ---> C pretty much trivially, I think.

I'm not sure I'd want to be marked on that explanation, but...

--
Jonathan Leffler (jleffler_at_earthlink.net, jleffler_at_informix.com)
Guardian of DBD::Informix 1.00.PC1 -- see http://www.cpan.org/
#include <disclaimer.h>