Re: Clean Object Class Design -- Circle/Ellipse

[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. 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 Received on Sat Aug 18 2001 - 10:20:24 CEST