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Re: Requirements for update languages?

From: Jan Hidders <hidders_at_REMOVE.THIS.uia.ua.ac.be>
Date: 13 Nov 2002 11:48:36 +0100
Message-ID: <3dd22e04$1@news.uia.ac.be>


Lauri Pietarinen wrote:
>> Be careful how you represent Date's words, because what you are saying here
>> is very false while what Date actually claims, "the CP of bags is not
>> well-defined in the SQL standard", is absolutely true.
>
>But he also states that "If you do try this exercise, I believe you'll find
>you're inevitably led into using the language of sets, not bags, in order
>to get around the errors and ambiguities."

Exactly. He says there that you probably need set terminology to define the bag cartesian product. Again something which is right on the dot. But that is definitely not the same as saying that it is impossible to define the bag cartesian product, which is false. If you're interested, here it is:

  B1 x B2 = { ( x, n+m ) | (x, n) in B1, (x, m) in B2 }

Received on Wed Nov 13 2002 - 04:48:36 CST

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