Re: Proposal: 6NF

Jan Hidders wrote:
> vc wrote:
> > Jan Hidders wrote:
> > > vc wrote:
> > > >
> > > > More interestingly, why bother with a trivial fact that Z may be
> > > > [considered] a subset of R in whatever sense ?
> > >
> > > Because you want a simple formalization of subtyping a la Cardelli and
> > > Wegner where subtyping coincides with being a subset. It means that the
> > > meanig of the + operation in (a + b) can be considered independent of
> > > the type of a and b.
> >
> > RIght, but my understanding of the OOP stuff leads me to believe that
> > a subtype should '"inherit" its type operations. If so, assuming R is
> > our base type, what do we do about division in Z (regarded as an R
> > subtype) ;) ?
>
> Call it integer division to distinguish it from the real division? :-)

Whatever you define as "integer division" cannot be claimed to be the division as understood in elementary arithmetic, as well as in abstract algebra, and therefore to be "inheritable" from R-division as I imagine it should be in the OOP sense of the word. In simpler terms, Z ain't a field while R is.

>
> -- Jan Hidders
Received on Fri Oct 13 2006 - 22:20:09 CEST