Re: Do Data Models Need to built on a Mathematical Concept?

> > I see a relation as a set(person).
>
> It is better to see a relation as a set of facts.
> A fact is a predicate - a true valued statement.

I would say it is even better to see a relation as a a set of things. The fact that the thing belongs to the set is all the fact that is required.
The fact that the thing belongs to the set is all the truth that is required.

> > Each tuple as an element(john, mary,..) of the set.
>
> Nope. A tuple is a fact.

Nope. A tuple represents a thing.

> > A tuple's attributes(gender,height) are properties of the element(john).
>
> Nope, (see next comment). We do have functional dependencies however, so the
> value Gender might be dependent on the value of FirstName in all the tuples in
> a relation.

I don't see what dependencies between attributes has to do with invalidating that attributes are similar to properties of a thing.

> > The tuple itself represents john
>
> If the attribute FirstName (of domain FirstNames) is a candidate key of the
> relation and "John" is a value of that domain, then I say it is OK to say that
> the value "John" represents john.

Nope, in such a case, the value "John" has uniquely identified the tuple which represents the real John.

> > and no one attribute of the tuple is john.
>
> Again, I say it is OK to take some domain, or set of domains, and say that an
> individual value of that domain(s) *is john*. This might be 'SSN', or some
> surrogate key or other, or in a simple database, just a FirstName.

Again, I say the value "John" or "SSN" has uniquely identified the tuple which represents the real John.

> >IMO, each tuple(row) can represents a thing in reality.
>
> Again, a tuple is a statement about things.

Again, tuple is a statement about one thing not things. Or a tuple says things about one thing not things.

> Neo, have you seen and understood Hugh Darwen's quote (slightly paraphrased)
> "Nouns are to Statements as Attributes are to Tuples"

What point are you trying to suggest?

> > A row itself in a table named Person represents a person,
> > regardless of how many attributes it has.
>
> Nouns are things.
> Attributes are things.
> Tuples and the relations that contain them are statements about things.

I really don't see much difference in our interpretation of the relational data model. Received on Tue May 06 2003 - 23:01:21 CEST