Re: Lots of Idiotic Silly Braces?
From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 21 Jul 2007 01:34:30 GMT
Message-ID: <Godoi.133654$NV3.124270_at_pd7urf2no>
>>Brian Selzer wrote:
>>...
>>
>>>Can rva's be keys? A relation value being the extension of a predicate,
>>>the set of tuples in a relation value represents a set of positive atomic
>>>formulae, and under the closed world assumption, that set implies the
>>>negation of each atomic formula that conforms to the schema but is not
>>>represented by a tuple. How, then, can a relation valued attribute be a
>>>key? Consider, the schema R{S{A, B}}, and the following relation value,
>>>r:
>>>
>>>r = {{S={{A=3, B=4}, {A=3, B=5}}}, {S={A=3, B=4}}}
>>>
>>>Now, suppose that P(A, B) is the predicate of S. The first tuple of r
>>>asserts that P(3, 5) is true, but the second tuple implies that P(3, 5)
>>>is false. ...
>>
>>I think "S" here is an attribute name, not a relation. S refers to two
>>different relation values which happen to appear as tuples in r. The first
>>tuple of of r asserts that the ("first", relation-valued) tuple that
>>combines (P(3,4) AND P(3,5)) is true in one relation value. The second
>>tuple implies that (P (3,5)) is false in the "second" relation value.
>>
Date: Sat, 21 Jul 2007 01:34:30 GMT
Message-ID: <Godoi.133654$NV3.124270_at_pd7urf2no>
Brian Selzer wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message > news:Lf4oi.131821$xq1.73460_at_pd7urf1no... >
>>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. ...
>>
>>I think "S" here is an attribute name, not a relation. S refers to two
>>different relation values which happen to appear as tuples in r. The first
>>tuple of of r asserts that the ("first", relation-valued) tuple that
>>combines (P(3,4) AND P(3,5)) is true in one relation value. The second
>>tuple implies that (P (3,5)) is false in the "second" relation value.
>>
>
>
> But that's the point. How can they both be true? And if they can, then how
> can it be consistent since there isn't also a tuple {S={A=3, B=5}}?
> ...
Those are the kind of questions that people who don't believe in Santa Claus ask. We are talking about the behaviour of a machine here, not mythology!
p Received on Sat Jul 21 2007 - 03:34:30 CEST