Re: Question on functional dependency

Many thanks to all the thoughtful replies.

You've given me much food for thought :)

Gerry

"Laconic2" <laconic2_at_comcast.net> wrote in message news:<2tidnYbcIsJBh87cRVn-hg_at_comcast.com>...
> "Josh Hewitt" <lajos.nagy_at_gmail.com> wrote in message
> news:1c92edeb.0409230805.6b331e9a_at_posting.google.com...
>
> > For example, in a relation on employees, usually the functional
> > dependency (FD) Emp# --> Dept# holds. Notice though, that we assume that
> > this is true because of the meaning that we assign to the attributes of
> > the relation: in the real world an employee is assigned to at most one
> > department.
>
> We all know about "assume", right?
>
> We don't have to assume that this is true. It's one of the questions we can
> ask during the analysis phase.
>
> If the FD is true in "the real world under consideration", the SME will be
> able to tell us.
>
> If you approach an existing set of data, and begin trying to find how
> normalized it is, it's a good, if somewhat back assward, way of finding out
> what the FD's really are.
>
> It's amazing how many times it's useful to do exactly this.
>
> One of the other things you get when you ask a programmer to design a
> database is, "we don't have to learn that much about the subject matter.
> We'll leave that for version 2."
>
> There ARE some programmers who can become excellent database designers,
> after suitable deprogramming. I consider myself a case in point. What gets
> most programmers in trouble on their first database design is that they
> think they already know how, when they don't.
Received on Sat Sep 25 2004 - 04:07:25 CEST