Re: Proposal: 6NF

vc schreef:

> Jan Hidders wrote:
> [...]
> > Is it really that hard to
> > understand that I was talking about two different ways of looking at
> > the same thing?
>
> Yes, it is hard. I'd rather prefer one be precise when one talks
> about that sort of things.

I'd say I was.

> I am actually puzzled when one sez, be it
> Cardelli or anyone else, subtyping is subsetting and then adds
> something like "Oh, by the way I am really talking about algebraic
> structures, not just arbitrary sets".

I said no such thing. The whole point was that there are two ways of defining certain data types, abstract algebraically and by direct construction of the sets. In the second approach subtyping equals subsetting, and I've discussed what the corresponding requirement in the algebra setting is. Neither of them is "what I'm really talking about" because both can be valid ways of modelling certain types.

> And I do not even want to get into the oddity of the idea that integers
> can be derived from reals, by subtyping or otherwise, essentially
> making reals somehow more fundamental (where do you get them from ?).

Why, from the class of surreal numbers, of course. :-)

But seriously, what does the order of derivation have to do with direction of subtyping? Surely you are not making the mistake of confusing inheritance, as a relationship that expresses that one thing is constructed in terms of another, with subtyping that expresses a conceptual relationship?

• Jan Hidders