Re: Plural or singular table names

"Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message news:bj4f8q$l0i$1_at_gazette.almaden.ibm.com...
> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:my65b.384$652.40534048_at_mantis.golden.net...
> > "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
> > news:bj2mh2$fri$1_at_gazette.almaden.ibm.com...
> > > BTW Could you show me how a constraint alters the meaning of a set
> > > of tuples? For me, a constraint alters the allowable set of
meanings, it
> > > does not alter the meaning of a particular set of tuples.
> >
> > Constraints identify the meaningful set of possible statements.
> >
> > Consider the following relation:
>
> Relation variable or relation value?

It doesn't matter. It is a relation with known constraints.

> > F:
> >
> > X Y Z
> > = = =
> > 2 2 4
> >
> > Do the following constraints give F different meanings?
> >
> > Z = X + Y
> > Z = X * Y
> > Z = X ^ Y
>
> If F is a variable then yes, if it is a value then no.
>
> Values do not have constraints, so constraints cannot alter their meaning.

Values do have constraints; they have types. The relation F with a binary key {X,Y} is different from a similar relation with a nullary key {}. A relation value has a predicate and a body.

> Either way it is values that have meaning, nothing else.

Constraints have meaning too.

> The meaning in these constraints
>
> Z = X + Y
> Z = X * Y
> Z = X ^ Y
>
> Is in the catalog relation values that define the operators.
>
> I.e. {X 2, Y 2, Z 4}
>
> does not tell me that say 2 + 2 = 4, it just tells me that "X 2, Y 2, Z
4"
>
> it would be say this tuple in the catalog
>
> { OperandA 2, OperandB 2, PLUS_Equals 4 }
>
> that tells me that "OperandA 2, OperandB 2, PLUS_Equals 4" which (to me)
is an non
> grammatical approximation of "2 + 2 = 4"

It might mean something to you, but it means nothing to the dbms. The constraint means something to both. Received on Wed Sep 03 2003 - 15:52:24 CEST