Re: Self pointer in limited record

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 05 Sep 2007 18:25:29 +0200, Jean-Pierre Rosen wrote:

> Dmitry A. Kazakov a �crit :

>> None of standard meanings 1-6 can be thought on the basis of single
>> instance. 
> 2 certainly can. The idea is that you cannot put "Spike the dog" into 
> your computer; what you can do is put some characteristics of it in the 
> form of data that are of interest from the point of view of your 
> program. You therefore abstract away all the uninteresting properties.

Yes, but my point is that these characteristics would have qualitative or
quantitative values from some sets. For example weight. Can I change it?
Would it be Spike? If yes, then what does the weight characterize? If not,
where is Spike? As long as I can construct (not Spike), it is not unique.
Alone the word "characterize" bears in it to distinguish, to mark ... among
some class of things.

>> The dictionary explicitly refers to "instances" and "examples."
>> Even treating abstraction exclusively as modeling with removing something
>> in order to model (though why couldn't we add something?)

> How could you have something in the model that is not in what you are 
> modelling?

I can add some properties to make implementation simpler or possible. This
happens quite often. For example, a telephone number modeled by a string,
function "+" with Constraint_Error added to its contract, imaginary part or
electric resistance. Some generalized problems are sufficiently simpler
than their constrained variants.

>> , even when
>> abstraction = moving from one substrate to another, one have to model not
>> only the object, but the relations it participates with other objects.
> But you can have relations between instances, not necessarily between 
> classes. If I walk Spike, it is a relation between an instance of a 
> human being and an instance of a dogan being :-)

Or an instance of a relation between human and dog. When you are designing
AdaControl, who walks Spike? (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de