Re: On Formal IS-A definition
Date: Sat, 08 May 2010 14:09:49 -0300
Message-ID: <4be59adf$0$12451$9a566e8b_at_news.aliant.net>
David BL wrote:
> On May 7, 9:36 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
>>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.
> > Values are immutable. Variables accessed by imperative programs are > usually mutable.
None of which has anything to do with what one may compose a set with.
<irrelevent philosophical dead-ends snipped>
>>>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 } ...
>
> No, that is not allowed. A dog is not a value.
You must have some set telling me what I may or may not have a set of. My set of three variables and a dog is a perfectly valid set just as Socrates is a perfectly valid element of a set of men.
Watch! I can even apply set algebra to my set. Suppose I have another set: the set of smells like skunk. I can interset the two sets to yield a third set: { Rosie }
So there!
<more irrelevancies snipped>
>>>>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.
> > Yes I agree that an operator is a symbol. What exactly does it mean > to "denote an operation"? So what does "operation" mean?
I suggest you check the standard vocabularies where the standard definition is given. Received on Sat May 08 2010 - 19:09:49 CEST