Re: On Formal IS-A definition

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 06 May 2010 22:23:49 -0300
Message-ID: <4be36ba6$0$12458$9a566e8b_at_news.aliant.net>



Bob Badour wrote:

> 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.

P.S. Sorry about the confusing cardinality switches. I've been burning the candle at both ends and I am over-tired. Received on Thu May 06 2010 - 20:23:49 CDT

Original text of this message