Re: Lots of Idiotic Silly Braces?

From: TroyK <>
Date: Fri, 20 Jul 2007 08:08:23 -0700
Message-ID: <>

On Jul 19, 11:54 pm, "Brian Selzer" <> 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.


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

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

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