Re: 4NF is Where It Is At! [WAS Re: 1:1 relationships]
Date: Tue, 13 Feb 2001 18:13:47 GMT
Message-ID: <vPei6.35402$2X4.107790_at_petpeeve.ziplink.net>
"Jan Hidders" <hidders_at_REMOVE.THIS.win.tue.nl> wrote in message
news:96bjhb$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? Received on Tue Feb 13 2001 - 19:13:47 CET