Re: Entity and Identity

From: David BL <>
Date: Wed, 22 Jul 2009 00:21:52 -0700 (PDT)
Message-ID: <>

On Jul 22, 12:57 pm, Brian <> wrote:
> On Jul 21, 11:15 pm, David BL <> wrote:

> > In your original statement you implied that location was part of an
> > object's state. That was the part I disagreed with.- Hide quoted text -
> I stated that a difference in location constitutes a difference in
> state.

I don't like that point of view. Typically the possible states of a state machine can be identified independently of the identity of the state machine. It then follows that it can be possible to say that two distinct state machine instances (i.e. at different "locations") happen to be in the same state at a given time.

> My line of thinking is that what is referenced by each object
> identifier is a particular object's state and that each object can
> have exactly one state at a time, so when there is more than one
> location at a given time, there is more than one state and therefore
> there must be more than one object.

You seem to be saying that a state machine *is* its (current) state. I would rather say that a state machine *has* a (current) state.

If you say that a state machine is its state, then when it's state changes it's not the same state machine. That doesn't make sense (because state machines can normally change states without losing their identity).

I think you're mucking up the simple (definitional) distinction between the "location" and "state" of an instance of a state machine that exists in some address space.

> The eight nodes in your cube of 1-
> ohm resistors are distinct even though they can only be distinguished
> relative to one another, and in the same way states at different
> locations are distinct, even if all of the fields in each state
> contain identical values.

That discussion will probably lead us into confusion between state machine and value! Received on Wed Jul 22 2009 - 09:21:52 CEST

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