Re: Lots of Idiotic Silly Braces?

From: paul c <>
Date: Mon, 23 Jul 2007 16:03:09 GMT
Message-ID: <1j4pi.2$_d2.0_at_pd7urf3no>

Brian Selzer wrote:

> "paul c" <> wrote in message 
> news:JzMoi.137922$1i1.132340_at_pd7urf3no...

>>Brian Selzer wrote:
>>>I think I see where you're going with this: correct me if I'm wrong, but
>>>aren't you saying that P and P2 are independent? ...
>>Maybe I would have been more on the point to say about your
>>r = {{S={{A=3, B=4}, {A=3, B=5}}}, {S={A=3, B=4}}}
>>that the two tuples of r, say s1 and s2, are independent relvars.
> Are you trying to say that each tuple in a relation value is independent of 
> all other tuples in the same relation?

I was trying to say that "primitive" operations on r, such as "delete" or "insert", don't operate on the tuples that appear in s1 and s2, they operate on the (relation) values of s1 and s2, which are the tuples that appear in r.

By the way, UNGROUP seems to have the effect of dispensing with the relation values of s1 and s2 and replacing them with the tuples that appear in s1 and s2. I presume this means that s1 and s2 must be of the same relation type, ie., same heading, otherwise UNGROUP would need to allow a result of more than one relation value, each value having different headings. Offhand, I don't know if there is a way to construct a relation that would have such relation values as tuples but if there is a way, then I think trying to UNGROUP it would be a problem!


p Received on Mon Jul 23 2007 - 18:03:09 CEST

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