Re: Clean Object Class Design -- Circle/Ellipse

>Once again (from my earlier post):
> RA is a field, whereas IA is only a ring
>and thus does nort preserve all properties of RA
>(existence of multiplicative inverse in particular).
>
>Is that enough of a proof that IA is not a subtype of RA
>(though Date would postulate that it is, since I is a subset of R)?

Assumptions, assumptions, assumptions!!!

Date argues that the type support of the DBMS must allow one to model a circle domain as a sub-type of an ellipse domain and you assume he claims one MUST model it that way. Likewise, the DBMS must allow one to model an integer as a sub-type of real, but that does not require you to do so.

If you decide that you want to call something integer such that n+1<=0 for some n>0, you have chosen to call something other than an integer by the same name. However, n+1>0 for all integer values, n, such that n>0 -- according to most people's understanding of integer and addition.

The fact that one can define the name Integer to represent a different set of numbers and to define the + symbol to have different behavior than addition does not prove anything about Date's understanding.

If I want, I can define a number system with the values { 1, 3, +, 7, b } and the operators { =, 2 }. Other than mental masturbation, what would be the point?

The fact that the DBMS must allow one to create either integer domain such that one is a sub-type of real and the other is not does not force anyone to do either!

Your claims regarding Date's understanding of type are extraordinary, incorrect and ad hominem. If you are going to make such an extraordinary claim, you must provide extraordinary proof, and you have failed to do so. Now, put up or shut up! Received on Sun Aug 05 2001 - 06:26:02 CEST