Patrick Cassidy wrote:
> It is an exaggeration to say that modeling a currency unit requires
> elaborate modeling of everything related.
There are two relevant questions:
(1) What aspects of the related concepts are needed to make the currency
ontology useful?
(2) What aspects of David's draft model (or some other draft of a uom
ontology) apply to them? (01)
Currency is a 'quantity kind', if you will, and I suppose one can talk
about 'particular quantities' that are instances of the Q1 of currency.
But there is no Q3, no amount that is independent of representation --
there are only quantity values. But the Q3 is the supertype of
'measurement unit'. So if the euro is a measurement unit, what abstract
amount of stuff in the currency dimension does it represent? How is it
defined? (02)
Currencies don't properly belong to a system of units that is related to
a system of quantities. Perhaps we could treat each national/regional
currency as a system in its own right. But conversion of units between
those systems isn't fixed. There is no conversion formula. As Pat says:
> There are multiple currency
> units, and between them there are exchange rates (which change daily),
And there are multiple financial instruments that are valued in
currencies and have different exchange rates based on the practices of
their respective markets. So the concept of "conversion of units" is
entirely different.
> and
> any number x times the base unit is indeed x multiples of the base unit, and
>
So the concept 'quantity value' seems to be properly supported, except
for how the base unit itself is defined.
> the way one 'measures' or 'standardizes' the base unit is as its value on
> any given day versus some one or more other freely exchangeable currency
> units, and one may also use the price of gold (on an open market without
> restrictions) as a measure of value.
I think that definition is circular. If every currency unit is
specified by its ratio to some other currency unit, we have the "turtles
all the way down" problem. At least one of them must be defined in
terms of something else, like a weight of specie (gold, silver, cows,
whatever). Unfortunately, I don't think any of them has been so defined
for years. (03)
"the price of gold (on an open market without restrictions)" is
fictitious. As Martin Weber observes, the actual realization process
affects the actual value. I suppose it might be specifiable with some
uncertainty, but it is hardly a fixed reference. We can argue about
whether measurement units are truly invariant, but there is no argument
about currency -- it is not. And that means that all the referential
concepts, and all the regulatory and industrial practices, that depend
on repeatability of measurements do not apply to currency.
> The 'measurement' method is a currency market,
which measures what property of what thing as a calibration point? Or
perhaps the question is: which currency market? Is there an
"international standard currency market" (the IMF? the World Bank?),
like the International Standard Kilogram?
> and for the same reason were are not going to represent measuring
> devices, we do not need to represent the details of a 'currency market',
> though a bare placeholder type may be useful. The only other ancillary
> concept we may want is an 'issuing authority', which will be a 'national
> government', which can also be a undefined placeholder. If we are going to
> represent the 'authority' that defines the base unit of physical measures,
> then defining the authority that issues a currency will be close enough to
> represent no problems.
>
So we are not going to model the concepts that give currency its meaning
and its utility, which goes to issue (1) above.
> If the majority prefer to exclude currencies from the UoM ontology, I have
> no objections, but I don't foresee major problems including currency.
I do. This is simply false analogy. Yes, currency is represented by
(number, unit), and that is the entirety of its similarity to units of
measure. Relative to issue (2) above, the rest of the ontological
concepts are doubtful or clearly inapplicable. What concerns me is that
the attempt to support this largely different concept might well cause
our ontology to be robbed of useful axioms, because they don't apply to
this extraneous case. And at the other end, we will surely provide
nothing of value to the finance industry. (04)
Rather than assuming that our ontology might apply to currency, I
suggest we build the ontology to address scientific and industrial units
of measure, and evaluate the applicability of the axioms to currency
when we are done. La prova e nel gusto -- the proof of the pudding is
in the taste. (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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