Re: Plural or singular table names

"Alfredo Novoa" <alfredo_at_ncs.es> wrote in message news:e4330f45.0309071531.6f887880_at_posting.google.com...
> "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
news:<bj59dh$13i2$1_at_gazette.almaden.ibm.com>...
>
> > > > Relation variable or relation value?
>
> In D&D books relation means value and relvar variable.
>
> > Nope, a type is part of the value.
>
> According to Date, values always carry with their type or types, but I
> don't think that a type is part of the value.

Every value has a set of types including a unique most specific type.

> I always carry with my wallet when I go out, but my wallet is not a
> part of me :-)

But your humanity is a part of you.

> > A relation value has no information about constraints. It might satisfy
certain
> > constraints, but it does not 'contain' any constraints. It might satisfy
A ->
>
> Agreed, and in TTM keys are not part of the relational types (at least
> in the examples), they are shorthands for database constraints which
> are part of the database type.

How, then, do the relational operations on values infer constraints?

> Tutorial D's relation type generator doesn't allow to declare
> candidate key constraints.

That's just a matter of shifting a couple productions around in the grammar.

> I find the idea of values having constrains as an absurd. Values are
> constants. We can not constraint a constant.

People do it all the time.

const float pi = 3.14159;
const unsigned int three = 3;

Even in TTM literals are typed, and types are constraints. Received on Mon Sep 08 2003 - 01:59:30 CEST