Re: Lucid statement of the MV vs RM position?
Date: 7 May 2006 17:54:35 -0700
Message-ID: <1147049674.976325.118020_at_j33g2000cwa.googlegroups.com>
Jon Heggland wrote:
>
> Perhaps I still was unclear; let me try again. Obviously you can
> postulate an aggregate operator that defined as iterated union, like SUM
> is iterated addition. Tutorial D does just that, and calls it (perhaps
> confusingly) UNION. You could call it GROUP instead, but Tutorial D does
> not. It uses the name GROUP for a unary relation operator that is
> shorthand for a particular extension/projection; alternatively a
> summarisation using that iterated union aggregate operator. I honestly
> don't see why this is so difficult to grasp.
You describe two things. You say they are different, but I don't see any differences.
One the one hand, we have "iterated union." On the other hand, we have "shorthand for a particular extension/projection", which is not very specific, but *could* be a description of what we have in the first case.
Can you be more specific about the differences between the two?
Marshall Received on Mon May 08 2006 - 02:54:35 CEST