John F. Sowa wrote:
> The VIM document is available at
>
> http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf
>
> EB> VIM is the International Vocabulary for Measurement, a publication
> > of BIPM -- the people who maintain the international standards for
> > units of measure. http://www.bipm.org/en/publications/guides/vim.html
>
The link I gave points to the PDF document, but it is the Web page for
the VIM and contains other useful references. (01)
> My only recommendation is to strengthen the following point:
>
> EB> It seemed like adopting their vocabulary would be good, and we
> > have tried to stay close to that.
>
> I would say we *must* stay *identical* to VIM as far as possible.
>
> That document is an international standard developed by professionals
> in the field who have collaborated with experts in all the R & D
> groups who use measures of any kind.
>
> Furthermore, it has undergone years of revisions based on feedback
> from experts around the world. They have very good reasons for
> every term and definition in that document.
>
>
I fully support this. (Being from NIST, I could scarcely do otherwise.) (02)
> And finally, if we develop a UoM ontology that differs from that
> document in any way, then our UoM is the one that is *wrong* --
> because all the users take that document as the Bible, not ours.
>
I take issue with this. The VIM is a standard vocabulary. It does not
represent itself as a formal ontology. In the VIM, concepts are
distinguished to the extent that the distinction is relevant to its
purpose. The VIM acknowledges that it makes multiple use of certain
terms, like "quantity", and it specifically elides certain concepts.
Our purpose is to construct a formal ontology which is useful for
applications other than measurement science. We cannot make multiple
use of a term, and we may find it necessary to separate concepts the VIM
elides, and perhaps to elide concepts the VIM separates. (03)
In particular, the VIM explicitly says that the magnitude of a quantity
is not knowable; it is only measurable, and every measurement involves
uncertainty. This is absolutely true, and it is the gospel of the
science. But it means that you cannot say that a stretch of roadway is
1km in length; you must say that it is 1km plus-or-minus 5 cm, if that
is the accuracy of your survey. And similarly, the label on your Coke
bottle that says "1 litre" and the label on your bag of potatoes that
says "10 lbs" is, according to the VIM, meaningless without additional
information. Now, we know that that information exists -- there are
regulatory and commercial requirements governing the allowable values as
determined by specified means of measurement (with correspondingly known
uncertainties). (04)
So, "ontologically speaking", how do we define a 'quantity value'? VIM
says it is "the expression of the magnitude of a quantity". I read that
to say that quantity value is the expression of an unknowable thing, and
therefore quantity values are used to distinguish unknowable things.
The VIM means, as others have said, that every 'quantity value' is
associated with a measurement, and it goes on to talk about how one can
compare measurements, which is not at all the same thing as comparing
quantity values. And yet, we compare quantity values all the time,
without apparent concern for the uncertainties of the associated
measurement process. The whole idea of 'magnitude' as an 'equivalence
class' relies on some notion of equivalence, e.g., of sticks having the
"same" length. It is rather like Newtonian physics: The factors that
we are ignoring are presumed to be insignificant to the purpose. (05)
So, in the same way that Newtonian physics is "wrong", but we can choose
to make an ontology for it, a practical ontology for units of measure
may depart from the VIM for reasons of practical usage. We just need to
document the departure when we make one, and explain why. (06)
[BTW, the above is my opinion, not that of NIST, and subject to being
outvoted by other more knowledgeable contributors.] (07)
> Of course, nobody is perfect, not even the VIM authors. But if
> we differ from them in any way, we have to be absolutely certain
> of our justifications, and we must report our changes to the
> committee that is responsible for the next version of VIM.
>
>
I'm not so sure about that. Are we making a formal ontology for
measurement science, or a practical ontology for units of measure? If
the former, and we find a need to clarify, extend or depart from, the
VIM, then John is quite right. If the latter, our purpose is different
from theirs, and our decisions may be irrelevant to the purpose of the
VIM. The trick is to avoid needless departures. (08)
> And by the way, I strongly recommend Annex A (page 68), which
> presents 12 "concept diagrams", which we should adopt as the
> guides for our ontology. If we find any discrepancy between those
> diagrams, the text of the document, and the requirements for a
> precise mapping to logic, we must report them to the VIM committee.
>
Yes, Annex A is one of the "candidate ontological models" that we should
be considering. (09)
-Ed (010)
--
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 (011)
"The opinions expressed above do not reflect consensus of NIST,
and have not been reviewed by any Government authority." (012)
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