Thanks. That is helpful. (01)
To restate: when we declare two units (e.g., furlongs and rods) to be of the
same dimension (length) we are saying they're comparable, without necessarily
knowing how they compare. (02)
I could live with that. (03)
I'll admit there is a part of me (probably the closed world part of me) that
says "don't even bother introducing a new unit of measure until you tell me how
it converts to at least one we know" But I suppose there is a use case for
allowing units with unknown conversions. (04)
> -----Original Message-----
> From: Pat Hayes [mailto:phayes@xxxxxxx]
> Sent: Tuesday, July 14, 2009 4:06 PM
> To: uom-ontology-std; Dave McComb
> Cc: edbark@xxxxxxxx
> Subject: Re: [uom-ontology-std] VIM definitions
>
>
> On Jul 14, 2009, at 4:33 PM, Dave McComb wrote:
>
> > Yes. This is what I was saying.
> >
> > So what do we call the "52 inches" " a quantity value that expresses
> a
> > magnitude without reference to a particular quantity"? does this
> > have a name?
> >
> > And I guess I'd continue where I was going with the thought about
> > "comparable"
> >
> > I think it takes more than being of the same kind to be "comparable"
> > if by being comparable we mean either that one is greater than the
> > other, or that they have a scalar relationship (Jupiter is 2 million
> > times as far away as your chair). Seems to me to be comparable we
> > need some unit in common and a conversion to it.
>
> Not at all. I can hold up two pieces of wood and say, this one is
> three times as long as that one. That makes perfect sense without
> mentioning units. (Yes, you can say that this is treating the shorter
> length as a 'unit' in a sense, but that sense isn't the usual one of
> "unit".)
>
> >
> >
> > Put another way, I think a furlong and a rod are both measures of
> > length. However I can't compare them until I can covert measures in
> > one either to the other or to something in common.
>
> You can't do the actual calculation until you have that, but you can
> say that there is some number N such that one of them is N times the
> other. And that is all the 'comparable' you need for the concepts to
> be defined. That is exactly sufficient and necessary for them to be of
> the same dimension.
>
> >
> > Am I missing something here?
>
> I think you are getting epistemic notions muddled with ontological
> ones.
>
> Pat
>
> >
> >
> >> -----Original Message-----
> >> From: uom-ontology-std-bounces@xxxxxxxxxxxxxxxx [mailto:uom-
> ontology-
> >> std-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ed Barkmeyer
> >> Sent: Tuesday, July 14, 2009 2:35 PM
> >> To: uom-ontology-std
> >> Subject: Re: [uom-ontology-std] VIM definitions
> >>
> >> Dave McComb wrote:
> >>> I took it to mean they were making a distinction between a
> >> particularly
> >>> measured thing (Johny is 4 feet tall) (which we call a measure)
> >>> and a
> >>> reference (you must be 52 inches tall to ride on the Thunder
> >>> Mountain
> >> Ride).
> >>> In the second case nothing was measured, someone just made up a
> >> reference
> >>> value.
> >>
> >> I don't think that is what is being distinguished in the secton of
> >> the
> >> VIM that David and Martin pointed to. The distinction in Dave's
> >> example
> >> is the one I was making between a 'particular quantity' and the
> >> abstraction of it that I attributed to the VIM term 'magnitude of a
> >> quantity'. The "52 inches" is a quantity value that expresses a
> >> magnitude without reference to a particular quantity.
> >>
> >>> The other distinction they were calling out "quantity in a general
> >>> sense" seems to me is just the TBox for the particular "dimension"
> >>> (i.e. "length")
> >>
> >> Yes. It is a T-box/class/category of particular quantities.
> >>
> >>> The points about being place in order, and grouping seem to refer
> to
> >>> the "dimension" (we can compare the length of the Themes to the
> >>> distance to the sun because they are both measures of distance
> >>> (or have dimension "length"
> >>
> >> Yes.
> >>
> >>> or even better both have a base unit of "meter" which really makes
> >>> them comparable)
> >>
> >> "comparable" is a source of confusion. The distance from the Sun to
> >> Jupiter is "comparable" to the distance from my chair to the door,
> >> full
> >> stop. That is because they are both quantities of the "length"
> kind.
> >> If one is expressed in astronomical units and the other in metres,
> >> the
> >> _quantity values_ are not directly "comparable" numerically --
> >> comparing
> >> the "numbers" is only meaningful when the "units" are the same.
> >>
> >> (I think this is what Dave was saying.)
> >>
> >> -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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> (05)
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