Matthew, (01)
I'm not sure I see the problem. (02)
Does it not dissolve if you distinguish between SKU_S3556 as an actual
physical part, with its individual characteristics and history, on the
one hand, and on the other hand P101 as a virtual placeholder for a
pump, with its position, connections, physical requirements and system
functions. Then SKU_S3556 isInPlace P101. Not so? (03)
There is doubtless a more usual set of nouns and verbs that Mechanical
Engineers habitually use for such situations, but some such set of
categories or types seems a starter move in a workable direction. There
are the usual conventional ways in which the final S-P fact above can
easily be given its 4D or temporal aspects. (04)
Or is the problem you've in mind deeper than merely the "a pump" / "the
pump" distinction? (05)
Regards,
Christopher (06)
----- Original Message -----
From: "Matthew West" <matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx>
To: "'Ontology Summit 2012 discussion'"
<ontology-summit@xxxxxxxxxxxxxxxx>
Sent: Sunday, January 29, 2012 1:48 PM
Subject: [ontology-summit] System Components (07)
Dear Colleagues, (08)
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. (09)
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. (010)
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. (011)
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. (012)
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." (013)
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." (014)
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." (015)
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. (016)
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. (017)
Ontologists need to step up to the mark here and provide proper
recognition for system components. (018)
Regards (019)
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/ (020)
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