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Re: [ontolog-forum] Ontological Means for Systems Engineering

To: Matthew West <dr.matthew.west@xxxxxxxxx>
Cc: "'[ontolog-forum] '" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Ed Barkmeyer <edbark@xxxxxxxx>
Date: Fri, 23 Jan 2009 13:31:39 -0500
Message-id: <497A0D0B.20103@xxxxxxxx>
Matthew West wrote:    (01)

>> This is a slight generalization of Matt's characterization, in that it
>> recognizes the existence of parts with subfunctions, without requiring
>> substitutability 
> MW: Can you give an example of a system with parts that were not
> substitutable?    (02)

I mentioned in fact that good systems engineering gives rise to 
subsitutability by encapsulating the mechanisms used by a subsystem and 
defining only their functions, interfaces, and constraints.    (03)

There are many examples, particularly in civil engineering, of systems 
with parts that are not substitutable, precisely because the engineered 
system was conceived as "one-off".  The analog is 16th-18th century 
European manufacturing, in which all parts were hand-made and 
hand-fitted.  (I think Eli Whitney is credited with developing the 
'standard parts' concept for his machines.)  The problem with all such 
systems is that they were ultimately designed incrementally, from a 
preliminary conceptualization of the system, rather than a system design.    (04)

I should also note that certain types of "design optimization", that 
combine part designs to perform multiple functions in one physical part, 
often create parts that are not 'substitutable' in the sense that any 
significantly different design could now perform the functions of that 
part in the system.    (05)

-Ed    (06)

Edward J. Barkmeyer                        Email: edbark@xxxxxxxx
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Stop 8263                Tel: +1 301-975-3528
Gaithersburg, MD 20899-8263                FAX: +1 301-975-4694    (07)

"The opinions expressed above do not reflect consensus of NIST,
  and have not been reviewed by any Government authority."    (08)

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