Re: By The Dawn's Normal Light

Laconic2 wrote:
> I claim that it's not useful to have one definition for "relation" for
> mathematics and an incompatible one for IT. On this point I agree with
> Dawn. And it's clear to me that the mathematical definition of "relation"
> does not force the values in the tuples to be atomic. And it's clear to me
> that the definition I always learned for 1NF does force the values in the
> tuples to be atomic.

I think it is useful to have separate definitions. Maybe the concepts should have been given different names though, but maths is littered with borrowed words that have different meanings in other contexts.

The motivating factor behind the development of relational database theory was first order predicate logic. It just so happened that the mathematical relation is a useful structure to model predicates.

The difference is down to first/second order logic I think. The fact that DBMS relations see their values as atomic is because: a) the relations specifically represent logical predicates, and b) the system is constrained to first-order logic only.

In maths, the relation is more abstract. It doesn't represent anything, it just *is*. So looking "inside" a value doesn't matter because we're no longer talking about first-order logical predicates.

So it's not the fact that database tables are mathematical relations that forces the values in the tuples to be atomic, it's the fact that those tuples represent first-order logical predicates

Paul. Received on Fri Oct 29 2004 - 13:35:09 CEST