# Re: Lots of Idiotic Silly Braces?

Date: Fri, 20 Jul 2007 08:08:23 -0700

Message-ID: <1184944103.418838.302910_at_n2g2000hse.googlegroups.com>

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