Re: 4NF is Where It Is At! [WAS Re: 1:1 relationships]

David Cressey wrote:
> "Jan Hidders" <hidders_at_REMOVE.THIS.win.tue.nl> wrote in message
> news:96bjhb$rfh$1_at_news.tue.nl...
> > Interesting example. What you describe is a dynamic database
> > constraint. But normalization usually only deals with static
> > database constraints. Because the constraint does not imply any new
> > functional dependencies (unless you introduce a column CO), it has
> > no impact on the normalization process.
>
> Can't the situation be described as a multivalued dependency? For
> the moment, let's leave the CO out of the model. I just included a
> description so that we who are discussing this can have a conceptual
> base for understanding the resulting relationship between phone
> numbers and addresses.
>
> In particular there is a set of addresses that are served by an
> office, and a set of phone numbers controlled by that office. That
> means that, given an address, I can't tell you specifically what the
> phone number is, but the address determines a set of possible phone
> numbers. Likewise, given a phone number, I can't tell you what the
> address is, but I can give you a set of possible addresses.
>
> Isn't this an example of a multivalued dependency?

No. Not even close.

For didactical reasons I will now let you do the work. :-) Here is the (simplified) version of the definition of an MVD:

  An MVD A->>B holds for a relation R(A,B,C) if for every tuple   (a1, b1, c1) it holds that if there is a tuple (a1, b2, *) then there   is also a tuple (a1, b2, c1).

So, now you can tell me which MVD you think holds, and explain to my why.

Good luck.

-- 
  Jan Hidders