Re: On Formal IS-A definition

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 07 May 2010 10:36:42 -0300
Message-ID: <4be4176d$0$12426$9a566e8b_at_news.aliant.net>

David BL wrote:

> On May 7, 9:20 am, Bob Badour <bbad..._at_pei.sympatico.ca> 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,
>
> Elements of sets are values, never variables.

I am unfamiliar with any restrictions on what goes in sets.

> You cannot talk about
> subset relationships between sets of variables because there is no
> such thing as a set of variables.

Of course there is. Suppose I have a set of 3 variables and a dog { a, b, c, Rosie } ...

>>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.

> 
> It's not clear to me what is meant exactly by an "operation" that acts
> on variables instead of values.  I would rather use the term
> "procedure" to avoid confusion with operators in algebraic systems.

Operation is well-defined both for procedural and declarative languages. Operators are symbols that denote operations per the ISO/IEC 2382 standard vocabularies. Received on Fri May 07 2010 - 15:36:42 CEST