# Re: On Formal IS-A definition

From: Bob Badour <bbadour_at_pei.sympatico.ca>

Date: Thu, 06 May 2010 22:20:24 -0300

Message-ID: <4be36ad9$0$12458$9a566e8b_at_news.aliant.net>

David BL wrote:

Date: Thu, 06 May 2010 22:20:24 -0300

Message-ID: <4be36ad9$0$12458$9a566e8b_at_news.aliant.net>

David BL wrote:

*> On May 6, 9:10 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:*

*> *

*> *

>>If one is interested specifically in subtypes of supertypes, a proper >>subset of a type with a proper superset of operations is a proper >>subtype of that type. Thus, circle values are a subtype of ellipse >>values and ellipse variables are a subtype of circle variables.

*>**>**> There is no subtype relationship between ellipse variables and circle**> variables (in either direction).**>**> Consider a procedure in an imperative language that is passed a**> reference to a circle variable. Most generally the variable can be**> used as an "in-out" parameter, meaning that the variable is both read**> and written by the procedure. An ellipse variable can only be**> substituted for out-parameters.*Ellipse variables are a proper subset of the variables where one might store a circle. It has a proper superset of the operations permitted for circle variables allowing one to also store a non-circular ellipse values.

Saying that one cannot apply circle value operations to ellipse variables demonstrates nothing more than a confusion between values and variables. One can apply all circle variable operations to ellipse variables. Received on Thu May 06 2010 - 20:20:24 CDT