Re: Clean Object Class Design -- Circle/Ellipse

In comp.object Martijn Meijering <mmeijeri_at_xs4all.nl> wrote:
> [posted and mailed]
>
> bbadour_at_golden.net (Bob Badour) wrote in
> <jZkf7.39$Pn.11203713_at_radon.golden.net>:
>
> [martijn] Don't get me wrong, I didn't say Date doesn't understand types or
> OO.
>
> [bob] Yes, that is exactly what you stated! ...
>
> [marc] You have demonstrated that you confused Martijn with me.
>
> [bob] While you did not state it directly, you clearly espoused the
> statement. You attempted to offer proof of the statement, and you denied
> that the statement is extraordinary.
>
> (I'm assuming you're talking to me now, not to Marc.) The original thread
> has disappeared from my newsreader, so I can't check the details, but I
> remember someone claiming Date doesn't understand types or OO.
>
> Discussions of the circle/ellipse type have been coming up every couple of
> months for years. One of the things that strike me about the discussions is
> that people aren't very precise about what they mean by type. You often see
> people offering the definition X is a subtype of Y if every instance of X
> IS-A instance of Y. That's not terribly precise, unless they tell us what
> the meaning of IS is ;-)
>
> The intuitive meaning many people seem to be using for subtype is simply
> subset. My point is that that is only one (the simplest) of many possible
> definitions. Subtype isn't a natural phenomenon, it's a matter of
> definition.

Subtype IS INDEED found in natural phenomena - at least in my world. it's just a matter of specifying for a given CONTEXT (DOMAIN) what is and what isn't a subtype.

Elliott

 What I'm interested in is which definition is the most useful,
> perhaps depending on the circumstances.
>
> Now, about the claim being extraordinary or not. Suppose someone said
> "Richard Nixon, Jimmy Hoffa, Antonin Scalia and Bill Clinton all have the
> Q37 property". Is that a true statement? No, it's a meaningless statement
> unless he tells us what the meaning of Q37 is. Is it an extraordinary
> statement? No, for the same reason, although it can be for sufficiently
> infuriating definitions of Q37. That's all I was trying to say.
>
> Regards,
>
> Martijn
 

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