Couldn't this be summed up as: (01)
Bridges fall down when: (02)
a. those building them do not build the necessary level of structural
integrity for the given set of requirements; or
B. the requirements for which the bridge have been designed/built did not
accurately capture the minimal structural requirements; or
C. an event happened for which the bridge was never designed to withstand
(larger earthquake, level 5 hurricane, fire/heat etc). (03)
Codifying knowledge is important to capture requirements. (04)
/d (05)
On 8/16/07 9:02 AM, "Ed Barkmeyer" <edbark@xxxxxxxx> wrote: (06)
> I only want to take up John Sowa's point about building bridges.
>
>> Engineers regularly build bridges that don't fall down.
>
> This is so because we have codified "knowledge" about the mechanics of
> structure that has been validated mathematically and by physical experiment,
> and has been accepted as "generally perceived truth" since about 1860. We
> also "know", from Einstein's work, that that codified knowledge is not
> entirely accurate, but it is accurate enough for the mechanics of bridges. It
> is not "reality"; it is a *model* of reality that has been proven to work. In
> fact, we can now reliably bound the difference between the model and the
> possible realities it represents.
>
>> Sometimes engineers build bridges that do fall down.
>
> This is so because there is more to the stability of a bridge than the
> mechanics of its structure. There is also the quality of the building
> materials and the nature of the terrain on which the bridge is being built,
> and the behavior of that terrain in times of varying natural phenomena.
> Bridges fall down because engineers don't always know enough about the actual
> materials and terrain and climate. And the famous Seattle bridge disaster
> occurred because of an acoustical phenomenon -- the wavelength of the
> vibration of the bridge in a high wind -- that had never previously been
> studied.
>
> So bridges stand because we have a certain amount of useful "knowledge" and
> they fail because we are not omniscient.
>
> When we build ontologies for public use, we have a responsibility to codify
> the knowledge that has been validated by theory and experiment, and to label
> that knowledge as such. It may not be "truth", but it represents a level of
> comprehension of our world that human experts accept and use, and we can
> hardly do better than that. Ontological engineering is not epistemology, and
> it is not metaphysics. But we do need a means of separating the "good" models
> (that generally produce results that can be validated by experiment) from the
> "bad" ones (that often produce nonsense).
>
> Finally, the bridge-building example teaches us that no ontology or
> combination of ontologies, no matter how well-founded, can be guaranteed to be
> *sufficient* for any given task. What you don't know can *always* hurt you.
>
> -Ed
>
> P.S. The World Trade Center is another example of the success of accepted
> knowledge and the disaster from the missing information. The impact of a
> jetliner at 480 knots did not bring down the twin towers -- one of the
> buildings swung 6 degrees off of vertical from the impact, but because it had
> been built to withstand earthquakes and hurricanes, it swung back to upright!
> What brought the towers down was the fact that the particle wind from the
> disintegrated aircraft stripped the heat insulation off the lateral supports,
> and the heat from the slow-burning office furniture then weakened the supports
> -- a combination of bizarre factors for which we only made the predictive
> model after the fact. (07)
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