Re: Plural or singular table names

"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?

> 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.

But if F was a variable, it would (in my view of the relational model) be the database variable (as that is the only variable I say we need in the model). If F is a database variable, then the value of F is different for each of the different constraints because it would contain different catalog constraint tuples.

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

The meaning in these constraints

    Z = X + Y
    Z = X * Y
    Z = X ^ Y

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"

!

Regards
Paul Vernon
Business Intelligence, IBM Global Services Received on Wed Sep 03 2003 - 12:17:18 CEST