Re: Lots of Idiotic Silly Braces?
From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 21 Jul 2007 20:48:07 GMT
Message-ID: <biuoi.135995$1i1.14227_at_pd7urf3no>
>> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>> news:Lf4oi.131821$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}}?
>> ...
Date: Sat, 21 Jul 2007 20:48:07 GMT
Message-ID: <biuoi.135995$1i1.14227_at_pd7urf3no>
> Brian Selzer wrote: >
>> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>> news:Lf4oi.131821$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 - 22:48:07 CEST