Re: MV Keys

In article <N5hPf.56961$dW3.6378_at_newssvr21.news.prodigy.com>, brian_at_selzer-software.com says...
> > Why? And what do you mean by "arriving at a list of widgits through the
> > use of the combinatorial rules of the universe"?
>
> I think I made my point clear earlier. The universe is the set of all
> possible values that are relevant to the discussion at hand and a set of
> rules for combining those values to form composite values, or propositions.
> Composite values are indeed propositions. If you have values A and B and
> group them together, then "A is associated with B" is a true statement.

I disagree. A value in itself is not a fact. In the context of the RM, only tuples in relations are facts. The cartesian point (2,3) is not a fact; the numbers 2 and 3 don't become more associated with each other just because I refer to this point. Only when it is put into a relation can it become (part of) a fact, e.g. "A FooBar is located at (2,3)".

> >> If you define constraints on the widgit list
> >> domain, but construct some widgit lists in a database without referencing
> >> that domain, then those constraints cannot be enforced for every list of
> >> widgits.
> >
> > So what? If you want domain constraints, you have to create a domain---
> > which is then distinct from other domains. I can create a domain of
> > integers between 42 and 5286; that does not preclude using integers
> > outside that range elsewhere in my database.
>
> You're missing the point. The whole numbers between 42 and 5286 are the
> magnitude of some class of values relevant to the discussion. Integers
> outside of that range must belong to a different domain.

Precisely. Just as lists that don't conform to your constrained widgit list must belong to some other domain.

> >> Without First Normal Form, there's no limitation on the complexity of an
> >> attribute.
> >
> > Nor is there *with* 1NF---but that might of course depend on you
> > definition of both "complex" and "1NF". How complex is a BLOB? An image?
> > A fingerprint? A video? I say any of these can be used as an attribute
> > value, and doing so doesn't affect 1NF.
>
> Only if they cannot be resolved into components that are part of the
> universe of discourse. It's important to differentiate between resolution
> and transformation, at least how I'm using the terms. A composite value can
> be resolved into component parts, meaning that an association exists between
> the component parts. A possible representation of a value can be
> transformed into another possible representation, but the value does not
> change. For example, a point can be represented using cartesian coordinates
> or polar coordinates, but it's still the same point: no information is lost.

I know, but I don't see the relevance. But since I don't accept your claim that a composite value constitutes a fact, it is pointless to belabour this point.

-- 
Jon