The art of ontology is the art of not designing something. What you're
suggesting looks a lot more like a design solution than a representation
of real things and the way they are. (01)
Mike (02)
ingvar_johansson wrote:
> A bit below comes a question from an informatics layman.
>
> Gunther Schadow wrote:
>
>
>> ingvar_johansson wrote:
>>
>>> one more comment. You asked:
>>>
>>>
>>>> 1 N.m = 1 N.m : true or false?
>>>>
>>> and I said 'true' (and so did Pat H). But this does not imply that 1 N.m
>>> of energy = 1 N.m of moment of force, since energy and moment of force
>>> are
>>> different kinds of quantities (despite having the same dimension).
>>>
>> and that's precisely my point and why I disagree with Pat Hayes
>> that this is not useful. I was asking if 1 N.m = 1 N.m and
>> the answer is ambiguous. 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.
>>
>> I don't want to discuss the N.m issue in particular at this
>> time, only that it's pointless to proceed if there is
>> disagreement about this matter.
>>
>> The question remains what we believe jointly that UoM concepts
>> should do for us. You may want them to preserve the difference
>> between torque and energy, I don't.
>>
>
> Can't you both cancel and preserve the difference? That is, can't you have
> both an over-arching concept 'nominal newton-meter' and a number of
> subsumed concepts such as 'energy newton-meter' and 'torque newton-meter';
> each of which brings in what VIM calls a kind-of-quantity?
>
> Ingvar
>
>
>> So the question remains
>> open on the list. But there is no point in proceeding if we
>> don't agree on this. We might, however, agree if we use these
>> example to be more clear about why we have the desire for the
>> UoM concepts to do what we want them to do and possibly how
>> else we might get our desires fulfilled.
>>
>> In my experience with dealing with scientific equations and
>> computations, the units were incredibly useful for (a) converting
>> to a unit that I needed and (b) giving assurance that I probably
>> didn't make some gross error in my equations. Thus, in my
>> experience with dimensioned terms it does not matter in the end
>> whether the m in N.m, was the length of a lever or a distance
>> of displacement, that is all in the concerns that led to my
>> equations. The units function more like a check-digit at the
>> end: if the unit term does not agree with the expected kind of
>> quantity, something went wrong in my calculation or the formula.
>>
>> 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.
>> 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. It does not do more nor
>> less than what the units do on paper. I.e., 1 N.m = 1 N.m
>> = 1 kg.m2.s-2 = 1 J.
>>
>> There is nothing you can do to separate these concepts unless
>> by assuming into your theory the detail of all of mechanics
>> (and all of science) which you can't do.
>>
>> BTW, it is not true that N.m of torque and joule of energy
>> are completely unrelated. Because the torque times angle
>> moved is again your energy. Whether or not we maintain a
>> dimension for angle in UCUM is also besides this point. Of
>> course: by adding more distinct dimensions we may be able
>> to preserve more distinctions and by having less dimensions
>> we lose distinctions that we can make by just looking at
>> number and unit. But because I do not expect much more than
>> the function of a "dimensional check digit" and defined
>> conversion rates from the units, I can give or take a few
>> dimensions without much trouble. The only place were I really
>> get into trouble is where we haven't even started to discuss,
>> i.e., idiosyncratic "procedure defined units".
>>
>> regards,
>> -Gunther
>>
>> --
>> 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
>>
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>
>
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> (03)
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