On Aug 5, 2009, at 8:39 AM, Joe Collins wrote: (01)
> Comments referring to the UML model:
>
> A given "particular quantity" is composed of a number and a reference.
>
> 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". (02)
I think this is not what is meant, if I understand the 'trope'
language. Take a concrete case, a measurement of length in meters and
two identical sticks A and B, with exactly the same length. There is
one property here, called "length", which applies to both sticks and
produces the same value in each case, say 3.1 meters. So: two sticks,
one property, one length value of that property. As I understand the
intention of the UML model, however, there would be two particular
quantities: the particular length of A and the particular length of B,
which are distinct, but have the same number and reference values
(respectively 3.1 and meter). (03)
(This illustrates why formalisms are so much more use than words, by
the way, when fixing this stuff. Words are ontologically floppy. For
another example, when you say, above, that something is "composed of"
a number and a reference, do you mean that it is literally the pair of
those things? Or that those are defining properties of it? Or simply
that those are properties of it? These would all give different
formalizations in an ontology.) (04)
>
> "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".
>
> n.b. - if you change any essential part of a measurement apparatus,
> like the
> unit, you change the numerical value.
>
> 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.
>
> 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.
>
> Perhaps a more succinct way of saying it is that a "generic
> quantity" is the
> *name* of a property (05)
No, don't say that. Names are lexical entities, not things like
quantities. (06)
Pat Hayes (07)
> and a "specific quantity" is the *value* of the property
> for a specific object.
>
> Regards,
> Joe C.
>
> 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
>>
> --
> _______________________________
> Joseph B. Collins, Ph.D.
> Code 5583, Adv. Info. Tech.
> Naval Research Laboratory
> Washington, DC 20375
> (202) 404-7041
> (202) 767-1122 (fax)
> B34, R221C
> _______________________________
>
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> (08)
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