Re: Proposal: 6NF

Jan Hidders wrote:
> vc wrote:
> > Jan Hidders wrote:
> > > vc wrote:
> > > But the constructions together with the operations that are defined
> > > along with them, *do* satisfy the expected properties.
> >
> > How would Q *without* division or Z *with* division (since that's what
> > you would have to do with at least one of them in order for the LSP to
> > work) satisfy what one expects from Q and Z in math ?
>
> Where do you get the strange idea that LSP requires that there should
> be a division within my defined Z that results in an element from Z?

Z does not have division.

> You keep on saying that, and I have no idea why you think that.
> Demonstrating that there is a problem should be simple. You could give
> a well-typed expression that has a certain result, and if you replace
> certain constants of type t1 in that expression with the corresponding
> constants in a subtype t2 then the result of the expression changes.
> Can you give me such an expression?

A, B and C are real;
D, E are integer;

C = A / B -- is OK
C = D / E -- the LSP requires that should be OK too but it is not because D / E is undefined. In the OOP mumbo-jumbo, the integer "class" does not have the '/' "method" (or does not understand the '/' "message").

>
> Since I think this is the core issue I'll limit my reply to this. I had
> actually written also replies to your other remarks, but we can always
> get to that later. It would be a pity if the discussion would grind to
> a halt because of discussion fatigue. :-)
>
> -- Jan Hidders
Received on Wed Oct 18 2006 - 21:40:22 CEST