Re: Object identity

On 30 Jun 2006 07:12:40 -0700, David Barrett-Lennard wrote:

Dmitry A. Kazakov wrote:
On 29 Jun 2006 19:03:17 -0700, David Barrett-Lennard wrote:


I was pointing out that merely saying that identity must be an
equivalence relation doesn't capture all the semantics.

Yes

Being an
equivalence relation is necessary but not sufficient. Perhaps I have
misunderstood you?

The point is, as I see it, that there is no any semantics of identity. We
cannot formalize it otherwise than by introducing some equivalence
relation.

The second point is that the identity defined on "self-values" (x=y) is no
better than an identity on some secondary values obtained from the
"self-values" (id(x)=id(y)), because in a software system we never have an
access to the "real" values of the problem space. What we call x=y is in
fact model(x)=model(y), which equalizes both.

I have trouble thinking of a critical section this way.
What's the entity that it represents?

Why? It is especially makes sense for things like critical sections,
hardware random generators, clocks etc, because their states are
fundamentally incomputable, i.e. you cannot describe their behavior in a
Turing-complete way.

This is interesting because paradoxically that's what I mean! We
*must* treat a critical section as an object-type. It doesn't make
sense to treat it as a value-type (which implies it maps under
interpretation to some entity outside the computing space). By
treating it as an object-type we are saved from the need to interpret
its state. Instead we are allowed to treat it as an object - a black
box that encapsulates identity, state and behaviour within a state
machine defined in the computing space.

It only shows that the issue is secondary to the original question about
self-things against model-things. To me all things are models, because all
values are outside the language.

Now it is always possible to define an isomorphism from a state machine
expressed at the level of instances in memory, to an equivalent,
abstract state machine. But what is the value in that? When
mathematicians have isomorphisms they (al least informally) blur the
distinction. That's why it seems rather silly to me to say that
instances of object-types aren't objects.

True, but that also blurs any distinction between "self" and "model".
Exactly because of this isomorphism. You cannot express the word "real" in
the language. So why do you care? There is nothing outside it.

OK, you could say that on some meta (incomputable) level there might exist
a difference. But that cannot be a reason for choice/comparison. Because if
this "non-isomorphic" component is sufficient, then *any* system won't be
able to capture it! All Turing-complete systems are, well, Turing-complete.

The bottom line, you need a much finer measure to judge about differences
between OO and RM.

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

Relevant Pages

  • Re: Object identity
    ... equivalence relation doesn't capture all the semantics. ... The point is, as I see it, that there is no any semantics of identity. ... the state machine is actually doing things on a real computer. ... interpretation to some entity outside the computing space). ...
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