Pat Hayes wrote:
>> I was asking if 1 N.m = 1 N.m and the answer is ambiguous.
>
> No, it is not. If you had asked whether 1 N.m moment of force = 1 N.m
> energy then the answer would clearly be no. But those are two different
> questions, not one ambiguous question. (01)
so we agree that 1 N.m = 1 N.m when we talk about units and there
is no such thing as "N.m momoent of force" as a unit? There is of
course the Quantity moment of force 1 N.m, but the unit is still
N.m without knowing anything about torque vs. energy. (02)
>> The unit is newton-meter, it is not
>> newton-meter-of-energy, therefore, I would argue, that the unit
>> is the same even if the kinds of quantity are different. Unless
>> we agree on this (by either one of us changing our mind) I don't
>> see a value at looking at ontological constructs.
>
> Well, we clearly agree. But I suspect we would have agreed if you had
> simply asked me this directly :-) (03)
If I remember correctly, I just asked "1 N.m = 1 N.m : true or
false?" (04)
>> The question remains what we believe jointly that UoM concepts
>> should do for us.
>
> That isnt necessarily a welldefined question to ask of an ontology, but
> my answer would be, to support a useful connection between the purely
> metrical notions of units, quantities and so forth and the wider
> medium-to-high level concepts of other ontologies, such things as
> 'physical object' and 'event'. (05)
Can you give examples for what that would mean? Just add to the
list of test cases. (06)
>> You may want them to preserve the difference
>> between torque and energy, I don't. So the question remains
>> open on the list. But there is no point in proceeding if we
>> don't agree on this.
>
> I disagree. If we try to establish agreement on the ultimate purpose of
> an ontology, we will never stop arguing. If it is any good, it will get
> used for things that we havn't yet imagined. That is part of the point
> of building it, in fact. (07)
All I am asking for is a list of test cases. This is not an
"ultimate purpose", just a list of statements which our ontology
should be able to affirm or deny. (08)
>> This is why around UCUM implementation I use the concept of
>> a "DimensionedQuantity". A Quantity is any set of values
>> where at least some values have a difference operation. A
>> DimensionedQuantity is essentially a number with a dimension.
>
> No, wait. Because it is *described* using a number and a dimension does
> not mean it *is* a number-dimension pair. In fact, it can't be. We have
> already established that we agree that 2.3 N.m = 2300 g.m2.s-2, and if
> that equation means what it says, then the same one of these can be
> described by two different number/dimension pairs. (09)
Where do you get two different number/dimension pairs from? Both
of them are the same in any one system of dimensions. (010)
2.3 N.m = 2300 m2.s-2.g = (2300, [2,-2,1,0,0,0,0])
2300 g.m2.s-2 = 2300 m2.s-2.g = (2300, [2,-2,1,0,0,0,0]) (011)
(2300, [2,-2,1,0,0,0,0]) = (2300, [2,-2,1,0,0,0,0]) (012)
same thing. (013)
>> Such a quantity for example is 16 N.m. Units are themselves
>> DimensionedQuantities with a name (and the name can be complex
>> such as N.m or even 16.N.m) So, my ontology behaves exactly
>> like the symbols that I write on a sheet of blank paper when
>> I compute my scientific equations.
>
> Again, that does not sound like good ontology engineering. It certainly
> does not generalize to more complex or more general situations. A
> description of a commercial transaction is not isomorphic to the actual
> transaction. (014)
I feel like you're taking out some realist bat on me now. What
does that have to do with the issue? I do not see units anywhere
but when I manipulate them on my paper. I don't encounter them
by any of my senses other than as constructs of the mind, I never
touched them. So whatever reality is the referent of those
symbols I experience through my symbols and I trust that that
reality behaves like what I am practicing when I manipulate my
symbols. (015)
Only the most privileged of us will be able to experience a
measuring with the metrologically defined "real" units. My
clock works using a quartz not a vibrating hydrogen atom, and
I measure distance using some tape measure, not a Caesium
wavelength-o-meter. (016)
So to me and most scientists it's rather irrelevant whatever
the metrological "reality" is behind those units. While the
idea is that all measurement standards are traceable to those
authoritative embodiments of them, practically this means little
more than that these authoritative embodiments are just
reconstructions of whatever the referent is of these units. (017)
That is also why the BPIM can choose to replace the embodiments.
Just as they redefine the second and the meter, they will one
day redefine the second again, and the kilogram also. But
whenever they re-define, they will choose some odd constant
factor so as to make sure that the new standard approximates
the referent of what we understand as the meaning of our unit
symbols. (018)
-Gunther (019)
--
Gunther Schadow, M.D., Ph.D. gschadow@xxxxxxxxxxxxxxx
Associate Professor Indiana University School of Informatics
Regenstrief Institute, Inc. Indiana University School of Medicine
tel:1(317)423-5521 http://aurora.regenstrief.org (020)
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