Re: What is Aggregation? Re: grouping in tuple relational calculus

"Paul" <paul_at_test.com> wrote in message news:42163d55$0$35759$ed2619ec_at_ptn-nntp-reader02.plus.net...
> Surely the associativity of a domain operator is orthogonal to the
> relation structure?

I disagree. Aggregate operator properties corelate with the relation agregation semantics.

> All it means is that your aggregate operator needs
> to have three parameters: (1) the column to aggregate, (2) an ordering
> to apply to the relation for the non-commutativity, and (3) an ordering
> to apply to the relation for the non-associativity. I think 2 & 3 would
> be independent of each other?

In case 3 it's no longer ordering. Without associativity you have to use brackets. Brackets naturally give rise to binary trees. Received on Fri Feb 18 2005 - 20:36:29 CET