Dear All, (01)
Ed wrote:
>IMO, "hardness" is a kind of quantity, but it won't bother me if our
>'units of measure ontology' does not support the Rockwell scale. I
>would prefer a cleaner ontology that properly supports numeric measures
>and uncertainty over bizarre concepts with useless axioms that are
>designed to support both SI and the Rockwell scale. (02)
Specific point: I am not sure that "hardness" has any precise meaning,
separate from the specific tests. Brinell hardness and Rockwell hardness are
not the same "kind of quantity" because they are not "mutually comparable"
except in the context of a family of similar material types. Therefore
hardness is not a single "kind of quantity". (03)
General point: There have been many ontologies which cover parts of the
domain for particular engineering applications, but they have not achieved
use outside these applications nor have they achieved engagement by the
metrology community. Our ambitions are larger, therefore I think that we
should at least know how to encompass these concepts. One of the main
customers for our work is likely to be the materials community, which I
believe is on the cusp of moving from materials data on spreadsheets to the
web based approaches pioneered by the life sciences. (04)
>The question is: Can we restrict our 'scales' and 'units' to the ones
>in which the quantity values are ratios? (OK, plus temperature.) Or do
>we define broad categories and then define the subcategories we really
>want to model and do those right? The problem I have with things like
>"hardness" is that I have no idea what subset of the useful axioms would
>include it. (05)
I do not see things like "hardness" as a problem - for some things the only
axiom is ordering. In the reasons given in "general point" above, I do not
think that we should restrict ourselves to simple quantities Q where were
are confident that:
a) r.q is in Q for all real r and all q in Q;
b) (r + s)q = rq + sq for all real r and s and all q in Q. (06)
Far from limiting our scope in this way, I suggest that we should extend it
to include position in space (and coordinate systems), and time. (07)
Best regards,
David (08)
At 18:53 06/08/2009 -0400, you wrote:
>Joe Collins wrote:
>> I agree with this except for the possible implication that "the VIM is
primarily
>> about making measurements of quantities" is an unnecessarily narrow
perspective.
>> The length of an object only has (physical) meaning when arrived at via a
>> measurement process.
>>
>I agree with that. I don't see how it contradicts the statement. I
>rather thought that "making measurements" is "measurement process". The
>VIM sees 'quantity' primarily as the 'property instance', the "trope".
>Those are the ones that have physical meaning. The abstractions are
>about assigning values to them by means of measurements.
>> ++++snip++++
>>
>>
>>>>> "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).
>>>>>
>>>>>
>>> I have several problems with this.
>>> First, quantity value is defined to be a number and a reference to a
>>> measurement _unit_.
>>>
>>
>> Not only that:
>>
>> "A reference can be a measurement unit, a measurement procedure, a reference
>> material, or a combination of such." (ISO/DIS 80000-1)
>>
>So your issue is about the fact that quantity values necessarily have
>associated uncertainties that are derived from their provenance? That
>is true, but it is the next step down the path. We are still trying to
>get past the question of which of "the height of the Eiffel Tower" or
>"183 metres" is what is meant by "quantity".
>
>If in DIS 80000 terms a 'quantity value' can be expressed in terms of a
>number and a measurement procedure, or a number and a reference
>material, then I will be of no help in using DIS 80000 as a basis for
>the ontology. But I will be happy to try to make sense of the draft you
>develop.
>> In the case of the kilogram, the standard, which defines the unit, is an
>> essential part of the apparatus. You cannot weigh something without it
(or one
>> of its "replicas").
>>
>The case of the kilogram is unique. The definition of the mole or the
>second or the metre has nothing to do with apparatus. Ergo, the
>generalization you stated is false. They are all referenced to specific
>physical phenomena, but the whole idea of the last 50 years is to
>reference them to invariant reproduceable physical phenomena, instead of
>specific artifacts or artifices. The kilogram is the last holdout of
>the 1876 approach.
>> All but one of the SI reference units are defined in terms
>>
>>> of an invariant physical phenomenon that can be measured in any
>>> laboratory with appropriate equipment. Moreover, the "best known
>>> procedures" (in terms of "smallest uncertainty") and the corresponding
>>> equipment have changed several times over the last 40 years, but those
>>> changes don't change the units. Changes in the apparatus produce changes
>>> (hopefully improvements) in the "uncertainty" of the measurement of the
>>> phenomenon.
>>>
>>
>> It is true that names of the units have not changed, but their
definitions have.
>> The only reason this does not present problems is because the newer
definitions
>> support greater precision and are made to be backwardly compatible with old
>> standards.
>>
>That is correct. The definitions of the units have become somewhat more
>precise, and in one case a different physical phenomenon was chosen.
>That is a consequence of improved measurement apparatus and the need for
>more precision for some modern applications. But, except for the
>artifact kilogram, none of the SI base units of measure is defined by
>reference to any apparatus. Each unit is defined by reference to a
>physical phenomenon that we can now measure better.
>
>The actual measurement mechanisms used for the local reference standards
>in the participating countries vary widely, with some consequences for
>international trade. There is a joint international activity (recently
>expanded) whose objective is to reconcile and align the results of the
>multiple technologies and practices. And this is not just the EU vs.
>Outer Slobbovia; this is U.S. v. Germany and India v. Japan. (This is
>also off-topic, but my point is that the units are not defined in terms
>of the practices, and the practices don't always agree.)
>> I do not think of the kilogram artifact as somehow a "less valid" standard,
>> though I agree it is certainly less convenient to distribute and does not
>> provide opportunity for improvement in precision.
>>
>>
>No one said it was "less valid". What I said was that it is the ONLY
>unit that is dependent on apparatus, which means that apparatus is NOT a
>common characteristic of units of measure.
>> <snip>
>>
>you can take the rest of this up with the metrology experts. NIST
>employs several hundred of them, but I ain't one.
>>>>> 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".
>>>>>
>>>>>
>>>>>
>>> The U.S. reference kilogram was made from the International Reference
>>> kilogram by polishing a slightly overweight copy of the artifact and
>>> comparing the magnitude on a very precise analytical balance. There was
>>> no 'scale' of the kind described here involved.
>>>
>>
>> Very precise, yes, but is not an analytical balance still a weighing scale?
>>
>It doesn't give "numbers". And the critical point here is that the
>magnitude of a quantity is independent of numbers. When you introduce a
>measurement unit, you then have a basis for a "number". But if you
>introduce a different measurement unit, you get a different number. The
>magnitude _is_; the quantity value _expresses_.
>> While not of identical design, many labs use scales that are design
variations
>> of the beam balance with mass standard.
>>
>Balances tell us what the relationship between two quantity magnitudes
>is: greater, equal, less. They don't provide numbers, and they don't
>depend on them. This constitutes a valuable insight in distinguishing
>'magnitude' from 'quantity value'.
>> If the reference kilogram is used to calibrate a mass measurement device,
is it
>> not then an essential part of the measurement apparatus? I do not think
it needs
>> to be permanently attached to be an essential part of the apparatus.
>>
>What the essential parts of a measurement apparatus may be is a topic
>that I am not qualified to address. And IMO, it is irrelevant to the
>work at hand.
>> I agree that supporting SI is most important.
>>
>Good. But we need to support other systems of units, and whole
>categories of derived units that we don't want to enumerate as well.
>
>The question is: Can we restrict our 'scales' and 'units' to the ones
>in which the quantity values are ratios? (OK, plus temperature.) Or do
>we define broad categories and then define the subcategories we really
>want to model and do those right? The problem I have with things like
>"hardness" is that I have no idea what subset of the useful axioms would
>include it.
>> (out of time for today)
>>
>> Joe C.
>>
>You and me both.
>
>Thanks, Joe.
>
>-Ed
>
>--
>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
>
>"The opinions expressed above do not reflect consensus of NIST,
> and have not been reviewed by any Government authority."
>
>
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> (09)
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CAESAR Systems Limited
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