Re: Lucid statement of the MV vs RM position?

Marshall Spight wrote:

> 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.

In the end, I think you and I focused on function while Jon focused on form.

Functionally, GROUP is an aggregate among other things. For instance, it is also a value selector.

Syntactically, Date and Darwen chose to handle it differently than other aggregates. Perhaps to avoid confusion with the UNION aggregate, or perhaps to provide a symmetric balance to UNGROUP. Perhaps for a lot of reasons or perhaps for no particular reason.

One can easily look at GROUP as a convenient shorthand for a combined type conversion and aggregate. Received on Mon May 08 2006 - 04:38:19 CEST