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

From: Paul <paul_at_test.com>
Date: Fri, 18 Feb 2005 19:08:03 +0000
Message-ID: <42163d55$0$35759$ed2619ec@ptn-nntp-reader02.plus.net>

Mikito Harakiri wrote:

>>Maybe it's not one you would use in practice but I'm sure there must be
>>examples that are more realistic - all you need is a non-associative
>>binary operator - maybe some matrix multiplication or something?

>
> Matrix multiplication is associative.

Ah yes I must be thinking of something else.

Well OK how about subtraction, division, exponentiation?

> If you drop associativity, then the underlying relation structure is no
> longer a set/list/bag. It seems to be a binary tree.

Surely the associativity of a domain operator is orthogonal to the relation structure? 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?

Paul. Received on Fri Feb 18 2005 - 13:08:03 CST