Re: Relation subset operators

Cimode wrote:
>
> While working on aggregation within groupping operations on the db
> core I design for relation manipulation, I questionned myself about
> the opportunity of using new operators to simplify relational division
> formulation and make it more systematic. For instance, conside the
> following questions:
>
> suppose CAR_SALE relation represented as
>
> CAR_SALE
> id car salesman price color date
> 1 Buick Henderson 10000 Red 01/01/1990
> 2 Buick Wilkinson 10000 Red 02/01/1990
> 3 Chevrolet Hutchinson 10000 Red 12/01/1990
> 4 Buick Wilkinson 10000 Blue 13/01/1990
> 5 Chevrolet Henderson 10000 Red 14/01/1990
> 6 Buick Henderson 10000 Blue 16/01/1990
> 7 Buick Henderson 10000 Blue 18/01/1990
> 8 Chevrolet Parson 10000 Yellow 18/01/1990
>
>...

Cimode, I'm struggling with this, trying to see the logical starting point. I would try to write this en francais but that would be incomprehensible, a teenage friend in France even runs rings around in English. I can't remember when I might have read about logical foundations of aggregate operators, but for me they've seemed to involve, necessarily, the equivalent of TTM group (I'm always a little leary of SQL GROUPBY because I gather it doesn't have a logical definition). Assuming a 1970-Codd-style relation there are many "SUM's" inherent in the above table/r-table/relation. To me, that 'inherency' seems similar to the transitive closures that are visible in some other relations. The examples I've seen elsewhere of TTM-style GROUP-ed attributes haven't offered any kind of operation that queries a subset of the tuples in a GROUPed value. So, if this makes any sense, from an algebraic viewpoint, I see aggregates as being very similar to TCLOSE, they must be applied first, before restriction. Are you following me?. Received on Thu Jun 04 2009 - 02:14:02 CEST