Re: Implementation of boolean types.

-CELKO- wrote:
> >> I have to say that I buy into Date's viewpoint: relations are predicates, and attributes are the variables of the predicate. <<
>
> I am more inclined toward thinking if them as facts.

A set of facts, then, instead of each predicate being a fact.

Isn't it common to think of the propositions and related tuples as (individual) facts and the predicates with variables (those in the header) as a way to see the set of facts that form the relation (feeding into the predicate logic, for example)? The propositions are instances of the predicates as tuples are elements of the relation. Am I getting my terms confused, are you, or is this another area where there is considerable variation within the discipline? Just curious.

> Facts are always
> "true" in the sense of existing. You do not talk about substitution in
> a set.

You do talk about instances, however, or values for a particular attribute. One way to look at it is that the propositions substitute a value for the header variable.

> Predicates can be true or false (or whatever other logical values your
> deductive system has). As Dave McGovran points out, SQL has no rule of
> inference, so it is not a logical system.

You're telling me! (smiles)

We even call them <search
> conditions> and not predicates.

But it would be helpful not to have the term predicate used for both the relation and each individual tuple in the relation. Is that what you are suggesting or did I misunderstand? Thanks. --dawn Received on Mon Jul 18 2005 - 07:30:10 CEST