Comments referring to the UML model: (01)
A given "particular quantity" is composed of a number and a reference. (02)
The "particular quantity" you refer to is what SI/VIM simply calls a
"quantity",
(not to be confused with "derived quantity" or "base quantity") defining it as
the "property of a phenomenon, body, or substance, where the property has a
magnitude that can be expressed by means of a number and a reference". (03)
"Quantity value" is most generally a number and a reference to a measurement
procedure. In the usual case where the quantity value is a (multiplicative)
product of a number and a measurement unit, the measurement unit refers to a
part of the measurement apparatus (the essential part).
For example, in SI, the unit "kilogram" is a reference to the physical artifact
stored by BIPM in Sevres, France. The measurement instrument, in this case a
weighing scale, is calibrated in terms of the reference. The kilogram standard
is the essential part of the measurement apparatus. The numbers that the
weighing scale gives for masses are the "numbers" referred to in the definition
of "quantity". (04)
n.b. - if you change any essential part of a measurement apparatus, like the
unit, you change the numerical value. (05)
When the quantities are expressible in terms of units, you generally can
multiply and divide the quantities, and commonly add or subtract them. In the
case of VIM example 7, Rockwell C hardness, forget about that. Hardness values
can only be ordered - products, ratios, sums, and differences are not valid. (06)
I believe that the VIM definition for "quantity" is most appropriate to your
"particular quantity".
The notion of "generic quantity" includes what SI/VIM calls "derived quantity",
"base quantity" and "quantity dimension", but a "generic quantity" never has a
numerical value. (07)
Perhaps a more succinct way of saying it is that a "generic quantity" is the
*name* of a property and a "specific quantity" is the *value* of the property
for a specific object. (08)
Regards,
Joe C. (09)
David Leal wrote:
> Dear All,
>
> Some comments have been added to the top level strawman UML model for
> quantities and units on
> http://ontolog.cim3.net/cgi-bin/wiki.pl?UoM_Ontology_Standard . These
> include brief discussion of the relationships with UnitsML, The Unified Code
> for Units of Measure (UCUM), Measurement Units Ontology (MUO), and the
> proposed Units of Measure extension to SysML.
>
> There seem to be no fundamental differences in approach as yet. The next
> step may be to derive an top level ontology and represent it in OWL and CLIF.
>
> Best regards,
> David
>
--
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Joseph B. Collins, Ph.D.
Code 5583, Adv. Info. Tech.
Naval Research Laboratory
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(202) 404-7041
(202) 767-1122 (fax)
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