Dear Pat,
Sorry for the delay in responding to this. A manic few days that did not
give me the time to give you a considered response. (01)
> 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. (02)
MW: Well let's look and see just what the parallels are. First if we start
with a performance of Shakespeare's Hamlet, then that is an activity, and
Shakespeare's Hamlet is a class of activity whose members are all those
performances. The performance of a part, is the participation of an actor in
that activity, in a role, for example Hamlet. Just as the performance of the
play is a member of the class of activity Shakespeare's Hamlet, the
performance by an actor of Hamlet is a member of the role Hamlet in the
play. Now we can say more that there is a constraint on the relationship
between the play, Shakespeare's Hamlet and the role Hamlet (both of which
are classes) such that each member of the play has a member of the role as a
part. (03)
MW: Now we can construct a similar structure around system and system
component. A system, of course, is not an activity. However, it is
reasonable to compare a system for the whole of its life with an activity
for the whole if its duration. So we will have system and class of system
and system component and system role, where a system component is the
component of the system, and a member of a system role. Finally, each
instance of the system would have a member of the system role as a system
component. For our P101 example, the class of system might be Crude
Distillation Unit Type 3, the system role might be Column 1 bottoms pump,
and the particulars would be Shell Haven CDU1 as the System, and P101 as the
Column 1 Bottoms Pump for CDU1. (04)
MW: Well fine, but this does not cover what I have been talking about, which
is when the physical pump is replaced in the same system component. The
proper parallel here with the play would be when Sir Laurence Olivier plays
Hamlet for the first act of a particular performance of the play, and then
Sir John Gielgood performs the second act, with further changes throughout
the cast. (05)
MW: Now I would not say that in this case the illustrious knights were
playing the same role. In fact they have definitely not played the same
role, or they would have been saying the same words in the same order. What
is happening is that they are playing different parts of a performance of
the role, and I would describe the relationship as one of whole-part, each
is playing a different part of the whole performance of the role of Hamlet. (06)
MW: And this indeed is why I think that system component is more properly an
individual than a class, and the pumps that are installed play parts of that
system role. (07)
MW: Of course, I will concede that there is a set of the different parts of
the performance of Hamlet by the two knights, but I would not think that
that set was the object of interest when considering the playing of the role
Hamlet in a performance of the play, and I do not think that the set of
installed pumps is the object of interest when I am considering what sort of
thing a system component is.
>
> 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..) (08)
MW: I agree. They are a different category of physical object. Apart from
the things you mention above they can also survive the complete replacement
of all their parts at once (as can the role of Hamlet when the actor is
substituted) and they can survive periods of non-existence. You don't find
something suitable in many 3D ontologies, though you do find them in at
least some 4D ones like ISO 15926, and probably IDEAS. The work Nicola and
his colleagues are doing is clearly moving in the direction I am showing
here, but the difficulties they are having clearly show the limitations that
3D ontologies have in their analytic power.
>
> You can identify a pump-phase (temporal slice) with a pump-role-phase,
> but you must not identify the actual individuals, so it's 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?
MW: Clearly not. What do you make of my analysis? (09)
Regards (010)
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/ (011)
This email originates from Information Junction Ltd. Registered in England
and Wales No. 6632177.
Registered office: 2 Brookside, Meadow Way, Letchworth Garden City,
Hertfordshire, SG6 3JE. (012)
>
> 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
> England
> > and Wales No. 6632177.
> > Registered office: 2 Brookside, Meadow Way, Letchworth Garden City,
> > Hertfordshire, SG6 3JE.
> >
> >
> >
> >
> >
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