So far this treatment works for me, and thanks to Joel also for his
well-worded suggestions earlier. (01)
OK, I'm going to go for a new list of "core concepts related to
units", incorporating these most recent statements. I think until
recently we had (02)
0) Units
1) Values with Units
2) The measurement event (this just adds the temporal dimension,
recognizing an event for the measurement)
3) The measurement method
4) The thing being measured (03)
And now I might nervously suggest something like the following: (04)
(A) Key Things in Our Ontology (05)
1) Dimension:
2) Unit:
3) Quantity: a value from the set of non-negative real numbers bound
together with a unit
4) Kind: a relationship between quantities wherein those quantities
can be converted among different units (06)
(B) Other things that are related (but not central?) [1] (07)
i) Measurement event: activity that assigns a Quantity to an entity in
the world [2]
ii) Measurement method: technique by which a Quantity is derived for
an entity in the world
iii) Measurable: thing in the world to which a Quantity can be assigned (08)
So if people provided clean definitions for 1 & 2, and turned 4 into
proper English, would we agree list (A) has the things we need to
capture in the unit ontology? (09)
John (010)
[1] Note that quantities can exist without measurements, so in group
(B) there are a bunch of activities not written down (like modeling,
estimating, calculating) that can produce quantities. (Because that
may be secondary to our goals, I'm not trying to make 3-5 exactly
right, but you might replace 'measurement' with 'quantization' and
measurable with 'quantifiable' if you wanted to push on that. (011)
[2] I am thinking 'entity in the world' may be physical,
computational, or of some other character, as long as it can have a
quantity. (012)
On Jul 21, 2009, at 1:26 PM, Joel Bender wrote: (013)
> I wrote:
>
>> So in our ontology there needs to be a way to say that "these units
>> belong to the same family" (inches, feet, meters, ...) or (radians,
>> angular degrees, ...) and "these do not" (energy, torque). I don't
>> think calling them dimensions is going to work because the term is so
>> heavily overloaded.
>
> Joe Collins wrote:
>
>> To be consistent with SI nomenclature, I urge you to use the concept
>> of "kind".
>
> and then later quoted the ISO standard:
>
>> Quantities of the same kind within a given system of quantities
>> have the same quantity dimension. However, quantities of the same
>> dimension are not necessarily of the same kind.
>
> So replace the word 'family' with 'kind', and to be more consistent
> with
> that document, replace what I called a 'decorated value' with
> 'quantity'.
>
> A quantity is thing that is a value from the set of non-negative
> real numbers bound together with a unit.
>
> And then:
>
> Two quantities are the same kind if there is exists a bijective
> function that allows quantities in one unit to be mapped into
> quantities in the other.
>
> And apparently this statement appears in multiple standards:
>
>> The division of the concept ‘quantity’ into several kinds is to some
>> extent arbitrary.
>
> But I think we can reach a consensus around a list that is a little
> more
> succinct than the examples listed, and still provide some flexibility
> where 'torque' is not 'energy'.
>
>
> Joel
> (014)
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