Re: more on delete from join

From: paul c <>
Date: Fri, 28 Aug 2009 17:45:40 GMT
Message-ID: <8JUlm.41207$Db2.18172_at_edtnps83>

Mr. Scott wrote:

> "paul c" <> wrote in message 
> news:WFTlm.41198$Db2.23941_at_edtnps83...

>> Mr. Scott wrote:
>>> "paul c" <> wrote in message 
>>> news:eimlm.40861$Db2.21494_at_edtnps83...

>> ...
>>>> I don't know if the plural 'disjunctions' is a typo'.  Do you mean that 
>>>> the resulting value of R stands for "r1 OR r2, etc." is true?
>>> I don't seem to be getting through.
>>> AND is to INTERSECTION as OR is to UNION.
>>> ,,,

>> That's a stretch, it would be more accurate to say that <AND> is to
>> relational intersection as <OR> is to relational union. If what you wrote
>> is what most people think it might help explain why so many want to
>> associate the result of a relational operation with the operations used
>> for form the result, even though the form of the resulting set of tuples
>> offers no way to record the operations that were used to produce it.

>> I think it is kind of phony for people to appeal at all to algebraic
>> operations in this way when the strict use of algebra can use <OR> to
>> produce a relation that is algebraically equal to one produced by <AND>.
>> That's why I sometimes say a union is always a join, even though it does
>> seem to wind people up. The expression used to form a view can be said to
>> persist only if it is recorded as a constraint, which I would say it
>> should be.
> I give up.  Instead of applying plain old ordinary logic, you appear to have 
> strange preconceived notions that are a mystery to me.  Without a common 
> frame of reference, there's no point in continuing this discussion. 

You could look at TTM Appendix A and ask why did D&D distinguish <AND> from logical AND. Probably they had several reasons, but the most obvious one would be so that they could avoid circular definitions. Received on Fri Aug 28 2009 - 19:45:40 CEST

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