# Re: Lots of Idiotic Silly Braces?

From: TroyK <cs_troyk_at_juno.com>
Date: Fri, 20 Jul 2007 08:08:23 -0700

On Jul 19, 11:54 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:

>
> Can rva's be keys? A relation value being the extension of a predicate, the
> set of tuples in a relation value represents a set of positive atomic
> formulae, and under the closed world assumption, that set implies the
> negation of each atomic formula that conforms to the schema but is not
> represented by a tuple. How, then, can a relation valued attribute be a
> key? Consider, the schema R{S{A, B}}, and the following relation value, r:
>
> r = {{S={{A=3, B=4}, {A=3, B=5}}}, {S={A=3, B=4}}}
>
> Now, suppose that P(A, B) is the predicate of S. The first tuple of r
> asserts that P(3, 5) is true, but the second tuple implies that P(3, 5) is
> false. It stands to reason that P(3, 5) cannot be both true and false.

<snip>

But it can be the case that P(3, 5) is true within the context of the first tuple,
and false within the context of the second. Substitute an integer- valued attribute
for the rva in the above example and check that it is the case that different
tuples in the relation can, indeed, have different values in the integer-valued
attribute.

TroyK Received on Fri Jul 20 2007 - 17:08:23 CEST

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