Re: Principle of Orthogonal Design

"Jan Hidders" <hidders_at_gmail.com> wrote in message news:febcf846-2d53-4979-af65-573b373ef6e9_at_l1g2000hsa.googlegroups.com... On 29 jan, 19:24, "Brian Selzer" <br..._at_selzer-software.com> wrote:

[huge snip]

> > Or are you saying
> > that there must always be an inclusion dependency of one sort or another
> > for
> > there to be a POOD violation?
>
> Yes, I am. You can verify this in the definition of the POOD rule I
> already presented to you.
>
> -- Jan Hidders

There is something about this that just doesn't seem right to me.

Suppose you have two second order predicates, p and q, such that

p(s(A, B), C) \/ q(s(A, B), D),

represented by database schema with relations

P {A, B, C}

    KEY {A}, and

Q {A, B, D}

    KEY {A}. Wouldn't there be meaning overlap between relations with those predicates regardless of whether there is an inclusion dependency?

Suppose that the FD A --> B on both P and Q is due to the predicate, s. Wouldn't that require that whenever there is a value for A that appears in both a tuple in P and a tuple in Q, the value for B in each of those tuples must also be identical?

This is not an example of dependency-induced overlap, since there is no stated dependency between P and Q, but in my opinion it is clearly a POOD violation. Received on Sat Feb 02 2008 - 16:45:13 CET