Re: Entity and Identity
Date: Thu, 23 Jul 2009 03:50:12 -0700 (PDT)
On Jul 22, 3:21 am, David BL <davi..._at_iinet.net.au> wrote:
> On Jul 22, 12:57 pm, Brian <br..._at_selzer-software.com> wrote:
> > On Jul 21, 11:15 pm, David BL <davi..._at_iinet.net.au> 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.
It may again be splitting hairs, but I would argue that it is the possible sets of field values rather than the possible states that can be determined independently, from the standpoint that a state is a set of field values /for/ a particular state machine and thus cannot be divorced from it. For there to be a state requires first that there be a state machine! It then follows that it can be possible for two distinct state machines to have equivalent, but not identical, states 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.
How did you come to that conclusion? If you look closely, what I actually said was "each object can *have* exactly one state at a time."
> > 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!
I don't think it will. There are state machines and there are values, and there are values for state machines. So you can have a state machine, o, and a value, v, and a value for a state machine (o,v). Received on Thu Jul 23 2009 - 12:50:12 CEST