Rijgersberg, Hajo wrote:
> 1. Maybe the most important question is (and probably only for my information
>and understanding): why do we base the vocabulary on VIM?
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
It seemed like adopting their vocabulary would be good, and we have
tried to stay close to that. (01)
> (I'm very interested in studying VIM, but couldn't find the document. Could
>someone please send me a link?) There are also other documents that we could
>base our vocabulary on.
>
Yes. For example, we could use the model in DOLCE or Cyc or SUMO or
some other published upper ontology that provides formal axioms for the
quantity and measurement concepts. We have a work item that says we
should look at these. (02)
> 2. But then I ignore VIM, and repeat myself: couldn't we have:
>
> "length of my table" ---"member of" ---> "length quantity"
> "length quantity" ---"subclass of" ---> "quantity"
>
> This is in accordance with some standard documents I know.
>
And it is in accordance with the model that David has produced. But he
uses "instance of", instead of "member of" ("instance" is an
"intensional" characterization; "member" is an "extensional"
characterization; although probably only an ontology purist would care.) (03)
>
> 3. Also, according to these documents, e.g. "1.3 metre" is not a quantity,
>but a measure.
Agreed. VIM calls it a "quantity value", which is an "expression of the
magnitude of a quantity". VIM uses "measure" to talk about a process
for determining a quantity value and for the results of that process. (04)
> (A quantity is like a variable, it is a reference to a value, like "1.3
>metre".)
>
We are careful to distinguish the class "quantity", whose instances are
particular quantities, like "the length of your table", from the class
"quantity magnitude", whose instances are the abstractions -- amounts of
length stuff. So if you have two chairs next to your table and they are
identical in size and shape, "the height of the first chair" is a
(particular) quantity, and "the height of the second chair" is a
(particular) quantity, and they are _different_ instances of "quantity",
but they have the same "magnitude". That is, there is one amount of
'length' that they both have. (05)
"1.3 metre" is a quantity value, which is an expression/name for a
"quantity magnitude". If your chairs are 1.3 metres high, then "1.3
metres" is a name for the magnitude of the height of each chair. And of
course, the same magnitude can have other names, such as "51 inches".
"51 inches" and "1.3 metres" are two different quantity values, but they
express the same "magnitude". That is the model we are proposing. (06)
But then there are two (or more) different classifiers that are called
"length". length-1 is a subclass of "(particular) quantity". The
length of your table is a length-1, the height of the second chair is a
length-1. But the magnitude of the height of the second chair is not a
length-1. length-2 is a subclass of 'quantity magnitude'. The
magnitude of the height of the second chair, which is the same as the
magnitude of the height of the first chair, is a length-2. So we must
choose one of these to be what we mean by "length". VIM is very clear
that it means length-1. But then we must not say that "1.3 metres
expresses a length"; we must say (as VIM does) that "1.3 metres
expresses the magnitude of a length". (07)
I personally think this usage is confusing for everyone. I would prefer
that we use "particular quantity" to be the class of things like the
height of the second chair, and use "quantity" to be what VIM calls the
"magnitude". But, on the other hand, you can't ever measure a
"magnitude"; you can only measure a particular quantity -- the height of
the second chair. The "magnitude" itself is not a physical phenomenon;
it is an abstraction. So it is very important that we agree on what
definition we choose for each term we use. Otherwise, everyone is confused. (08)
> Again, hopefully this discussion is appreciated; it is meant to be
>constructive, with the aim of working together to achieve a high-quality
>vocabulary.
Me, too. But we keep going around these same issues, because people
don't understand the definitions. (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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