Re: Is relational theory irrelevant? (was Re: Dreaming About Redesigning SQL)
Date: 13 Nov 2003 01:56:51 -0800
Message-ID: <51d64140.0311130156.6c376b59_at_posting.google.com>
"Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message news:<DxBsb.30$1n1.179_at_news.oracle.com>...
> > Ordered domains do have logical order. Relations have no order, but the
> > values in the relations have order.
>
> That totally depends whom you ask, of course. A person with mathematical
> background would have no trouble defining an order relation among the tuples
> of the original relation induced by the order defined on each domain
> associated with individual column.
I think the answer is due to the intended "real-life" meaning of
relations.
Clearly in general a set can have an ordering defined on it.
But a relation isn't just any old set, it is a set of *logical
propositions*.
So:
- the grass is green.
- the sky is blue.
means exactly the same as:
- the sky is blue.
- the grass is green.
i.e. P1 AND P2 = P2 AND P1
where P1, P2 are the propositions above. So you could say the fact that relations can't have an order comes down to the commutativity of the logical AND operator.
Paul. Received on Thu Nov 13 2003 - 10:56:51 CET