> Very good question, Matthew. Let me try out an idea on you. Your P101 is
> actually a role played by a pump, rather than a pump itself. Think of it
as
> being like Hamlet, as played by Lawrence Olivier (P101 as played by
S3556).
> You can change actors, and Hamlet is still Hamlet - same role - and while
> Olivier is playing the role, he *is* Hamlet, at least in a sense. But this
second
> "is" cannot be identity, since you can kick the actor, but you can't kick
a role.
>
> Both a pump and a pump-role are spatiotemporal entities, but they have
> different identity conditions. The identity of a pump, like any other
physical
> object, is determined by the disposition of pieces of material stuff
(metal,
> plastic, rubber), but the identity of the role is determined by its
interfaces to
> the rest of the system (being connected to this pipe in this place and
> operated by this controller, etc..)
>
> You can identify a pump-phase (temporal slice) with a pump-role-phase, but
> you must not identify the actual individuals, so its safer to actually
have a
> relation of 'functioning as' of the like to attach a role-playing thing to
its role.
> Or, you can treat the role as a time-dependent property of the physical
thing,
> but you will probably need a CL-style ability to have properties of
properties
> if you go that (elegant) route.
>
> Make sense?
>
> Pat
>
>
>
> On Jan 29, 2012, at 3:48 AM, Matthew West wrote:
>
> > Dear Colleagues,
> >
> > Last Thursday I complained that most ontologies do not give adequate
> > treatment to what I call system components, and if ontology is going
> > to gain traction within the systems world, it needs to get a better
> > understanding of this central idea in systems engineering.
> >
> > I illustrated the issue by telling the (simplified) life story of a
> > system
> > component: the pump, P101, at the bottom of a distillation column.
> > Here is its story.
> >
> > The designer creates a drawing of the distillation column including at
> > the bottom of the column a pump to pump away the column bottoms. He
> > labels it P101, decides that one pump will be sufficient, and gives
> > the specification for the pump in terms of Net Positive Suction Head,
> > differential head, flow rate, materials of construction, and many other
> things.
> >
> > The construction engineer picks up the drawing and specification and
> > notices he has to install a pump as P101. Fortunately, he has a pump
> > in stock from a previous project, that has been in stores unused for 5
> > years which exactly meets the specification. On it is stamped Serial No
> S3556.
> >
> > The designer and the Operator comes to see the pump be installed, and
> > once the connections are made, he gives the pump a friendly kick and
> > says to the construction engineer "It's good to see P101 realized at
> > last". The construction engineer says in return "Yes, and it's good to
> > get S3556 off my hands at last." He turns to the operator and says
> > "Why don't we change your drawings to show S3556 instead of P101?" The
> > operator says "No, don't do that, it's a replaceable part, and one day
> > another pump will be put there, and I don't want to have to change all
> > the drawings and other documentation that refers to P101 each time it
> > is replaced, as far as I am concerned it's the same pump whatever is
> installed there."
> >
> > Some time later the pump breaks down and needs to be taken back to the
> > workshop. The maintenance engineer says to the operator "Hi, can I
> > take
> > S3556 installed as P101 back to the workshop?" The operator replies
> > "Sure, but what am I supposed to do without my P101? If it does not
> > exist I cannot operate my distillation column." The maintenance
> > engineer responds, "I understand. We have another pump S4567, that
> > meets the same specification as P101. We'll replace S3556 with it and
> > you will only be without P101 for a few hours. I don't understand how
> > you can continue to call it P101 though when all the parts have
> > changed at once." The operator replies "I don't care about that. What
> > I care about is what is connected in my system to pump the liquid from
> > the bottom of the column. As long as it does that, it is P101 to me."
> >
> > Later the distillation column is demolished. The operator says, "A sad
> > end, I was very fond of P101, but it is no more." The demolition
> > engineer says, "Yes indeed. Fortunately, we can take S4567 and use it on
> another plant."
> >
> > It's probably worth summarising the key characteristics of a system
> > component:
> > - It comes into existence the first time it is installed.
> > - It is identical to the equipment items installed, whilst they are
> > installed (but not before or after).
> > - It can survive complete replacement of all its parts at once.
> > - It can survive periods of non-existence.
> > - It ceases to exist when the system it is a component of ceases to
exist.
> >
> > This is clearly rather different from the life of ordinary physical
objects.
> > However, relatively few ontologies recognise that such things exist.
> > Many try to fob system components off as being classes, or abstract
> > individuals, though these clearly do not have the required
characteristics.
> >
> > Ontologists need to step up to the mark here and provide proper
> > recognition for system components.
> >
> > Regards
> >
> > Matthew West
> > Information Junction
> > Tel:
+44 1489 880185
> > Mobile:
+44 750 3385279
> > Skype: dr.matthew.west
> >
matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
http://www.informationjunction.co.uk/
> >
http://www.matthew-west.org.uk/
> >
> > This email originates from Information Junction Ltd. Registered in
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> >
> >
> >
> >
> >
> >
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