Dear Henson, (01)
I agree with your comments, but the terminology is difficult. See: (02)
ISO 31-0:1992 - Quantities and units - Part 0 - General principles, Clause 2.1: (03)
"Physical quantities may be grouped together into categories of quantities
which are mutually comparable. Lengths, diameters, distances, heights,
wavelengths and so on would constitute such a category. Mutually comparable
quantities are called "quantities of the same kind." (04)
"If a particular example of a quantity from such a category is chosen as a
reference quantity called the <em>unit</em>, then any other quantity from
this category can be expressed in terms of this unit, as a product of this
unit and a number." (05)
>From this I deduce that:
- The length 2.3 m is a "quantity".
- Length is a "quantities of the same kind". The synonym "quantity category"
is also used implicitly used in the text. (06)
I don't think that the ISO 31-0 terminology is ideal (I do not know whether
ISO 80000 is the same). However, it is important to have an onotology which
uses the same terminology of the standards from which it is derived. This is
why it is necessary to have ISO TC12 on board. (07)
The second paragraph worries me - this is true for some "quantities of the
same kind", but not others. Perhaps after discussion we can define the
subclass of "quantities of the same kind" for which this is true. (08)
Best regards,
David (09)
p.s. I have take the liberty of cc'ing this to the ontology summit to see if
the discussion "rings any bells" with others. (010)
At 11:05 08/05/2009 -0500, you wrote:
> Dear David,
>This is the beginning of a good idea. My comments will be a bit random
>as I have not been thinking about this lately. However in answer, I
>believe that length is an example of what upper ontologies call a
>Quantity. Length would be a specialization of quantity. Quantity is
>what I belive is called a "reaified" class. Quantities can be
>measured/computed in various ways using different kinds of units. I
>believe that a meter is a unit of length measurement. We have had a lot
>of discussion of this stuff which I have forgotten. What I say may be
>wrong, but perhaps it will prompt you to take the next shot at it. I
>believe that upperontologies use "haslength" as a role that takes a
>value in the length quantity space, and haslengthinmeters is the
>composition of haslenght and some "coordination function" defined on the
>quantity which takes numeric or ordinal values. Let me know what you
>think
>Regards
>- Henson
>
>-----Original Message-----
>From: David Leal [mailto:david.leal@xxxxxxxxxxxxxxxxxxx]
>Sent: Friday, May 08, 2009 10:52 AM
>To: Graves, Henson; vicki.bailey@xxxxxxxxxxxxxxxxxxxxxx
>Subject: RE: [ontology-summit] Progressing a Units Ontology - Now
>
>Dear Henson,
>
>Perhaps we would start with the statement: "The metre is a unit of
>length."
>
>1) What sort of thing is "length"?
>
>2) What sort of things can have a unit?
>
>3) What does "unit of" add to the statement "The metre is a length"?
>
>4) In the statement "The metre is a length", what does "is a" mean?
>
>With an agreed answer to each of these, I think we would be near a first
>deliverable.
>
>Best regards,
>David (011)
============================================================
David Leal
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============================================================ (012)
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