Re: An alternative to possreps

From: Erwin <e.smout_at_myonline.be>
Date: Wed, 8 Jun 2011 03:08:00 -0700 (PDT)
Message-ID: <dfde7cfc-d8d1-446b-99e7-0941c7e1608b_at_n11g2000yqf.googlegroups.com>


On 8 jun, 03:55, David BL <davi..._at_iinet.net.au> wrote:
> On Jun 7, 9:49 pm, Bob Badour <b..._at_badour.net> wrote:
>
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> > David BL wrote:
> > > On Jun 6, 9:26 pm, Erwin <e.sm..._at_myonline.be> wrote:
>
> > >>On 31 mei, 11:54, David BL <davi..._at_iinet.net.au> wrote:
>
> > >>>Is there anything in TTM that prohibits one from making every type a
> > >>>dummy type?  Would that make it essentially the same approach which
> > >>>I've described?
>
> > >>Not "in TTM".  What prohibits this is "reality", I'd rather say.
>
> > >>If you're interested in a subset of T, then you can't define this
> > >>subset by means of UNIONs involving T.
>
> > > Yes, but that is not a problem.  Let Ellipse be a "dummy type".  If
> > > you're interested in a subtype Circle of Ellipse then you can simply
> > > declare Circle as another dummy type. I'm assuming you can declare
> > > subtype relationships between dummy types.  In my approach you use
> > > these declarations:
>
> > >     type Ellipse;
> > >     type Circle;
> > >     Circle isa Ellipse;
>
> > > I consider types like Circle and Ellipse to be defined by their
> > > operators.  In that sense there is no problem treating all types as
> > > "dummy types".
>
> > Either the operators define the equivalent of possreps or the type model
> >   doesn't really describe ellipses and circles. So what are you trying
> > to achieve?
>
> I'm suggesting the operators define the equivalent of possreps.
> Possreps are redundant.
>
> The equality operator has a role to play in this.  The possrep
> constraint which specifies which representations of ellipses are
> circles is instead defined indirectly by the equality operator (which
> defines which representations of ellipses are equal to some
> representation of a circle).- Tekst uit oorspronkelijk bericht niet weergeven -
>
> - Tekst uit oorspronkelijk bericht weergeven -

I definitely prefer to see the rule that determines whether or not an ellipse is a circle, stated explicitly as part of the declaration of CIRCLE, rather than having to go digging in the details of the equality operator (or even worse, in its implementing code).

Plus, circles-and-ellipses are only in the realms of the inheritance model. Possreps also have a role to play without inheritance. Received on Wed Jun 08 2011 - 12:08:00 CEST

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