Re: ontology for units of measurement and/or physical quantities

Hi,

In "Time Ontology in OWL"(hereafter TMO),  
a property time:hasDurationDescription is introduced 
to link a TemporalEntity to a DurationDescription, and
time:hasDurationDescription is not defined as functional,
to allow variants of description.

And this approach differs from what Tim suggested.

Following that approach, the mass case would be

:box1 exterms:hasMass
	[a exterms:Mass;
	 exterms:hasMassDescription 
		[a exterms:MassDescription;
		 exterms:kilogram 2.4],
		[a exterms:MassDescription;
		 exterms:gram 2400.0],
		[a exterms:MassDescription;
		 exterms:kilogram 2.0;
		 exterms:gram 400.0]
	].

And exterms:hasMassDescription is not functional,
although exterms:hasMass is functional.

I guess exterms:hasMassDescription here is what Danny meant by
exterms:massMeasure.

The approach above seems a little bit complex,
but there seems to be cases where that approach is convenient.

For example, if one wants to say that height of box1 is 1 feet 1 inch,

in the TMO approach, the description would be

:box1 exterms:hasHeight
	[a exterms:Length;
	 exterms:hasLengthDescription
		[a exterms:LengthDescription;
		 exterms:feet 1.0;
		 exterms:inches 1.0]
	].

while in the approach by Tim, the description would be

:box1 exterms:hasHeight
	[a exterms:Length;
	 exunits:inches 13.0;
	 exunits:feet 1.08333].

13/12 = 1.08333...

Which approach one should take could depend on the
application, but it seems a Note would be useful
as the reference for ontology developers and users.
(in Semantic Web Deployment Working Group?
Danbri suggested an XG)[3]

BTW, this example shows an issue that we might need
some means to express fractions...



[3] http://lists.w3.org/Archives/Public/semantic-web/2006Sep/0113.html

Best,
Yoshio


On Fri, 29 Sep 2006 00:38:22 +0200
Danny Ayers <danny.ayers@gmail.com> wrote:

> 
> On 28/09/06, Tim Berners-Lee <timbl@w3.org> wrote:
> > While
> >        box1  exterms:mass  [ex:value  2.4; exterms:units
> > exunits:kilograms] .
> >
> >   might seem like a straightforward way, it turns out it is a trap!
> >
> > Presumably this one could write too
> >
> >        box1 exterms:mass  [ex:value  2.4; exterms:units
> > exunits:kilograms] ;
> >            exterms:mass  [ex:value  2400.0; exterms:units exunits:grams] .
> >
> > You would expect mass to be a functional property, to the two Bnodes
> > must
> > be owl:sameAs each other, so we can conclude that the masses are the
> > same:
> >
> >        box1 exterms:mass  [
> >                         ex:value  2.4;
> >                         exterms:units exunits:kilograms;
> >                         ex:value  2400.0;
> >                         exterms:units exunits:grams]
> >
> > bzzzt! tilt! that means we have a mass with two values and two units.
> 
> Nice catch. exterms:mass in the original example would maybe have been
> better named exterms:massMeasure, to avoid the (natural) expectation
> of it being a functional property.
> 
> > A much *better way* is to use the unit as a connecting predicate.
> >
> >        box1  exterms:mass   [ exunits:kilograms 2.4 ].
> >
> > You can then write quite validly
> >
> >        box1  exterms:mass   [ exunits:grams 2400.0;
> > exunits:kilograms 2.4   ].
> >
> > This takes less space and can be easily manipulated, and doesn't
> > throw up
> > horrible errors.
> >
> > A unit kg is the relationship between 3kg and 3.
> 
> Yup, that looks a lot better.
> 
> [snip]
> 
> > PPS: can't you even say, using units predicates as multiplication or
> > division of scalar quantities
> >
> > @prefix : <....exunits#>.
> > @keywords.
> >
> >    box1  height 3 ^ m ;
> >         speed   3 ^ m!s ;
> >         acceleration 9.81 ^m!s!s .
> 
> Not sure I grok what you've got there, is ! a predicate (on the
> literal) as "per"? (Is this all N3?)
> 
> In the defence of, er, the devil, I'd have to note that the source of
> the example, the RDF Primer[1], doesn't cover the layer which includes
> functional properties (is the approach a reasonable
> model/approximation? Ok,  your point above says not). Can't help but
> notice too that the doc "has been endorsed by the Director as a W3C
> Recommendation"...
> 
> (does the n-ary relationships note [2]  cover this I wonder?)
> 
> Cheers,
> Danny.
> 
> > > [1] http://www.w3.org/TR/swbp-n-aryRelations/
> > > [2] http://www.w3.org/TR/rdf-primer/#rdfvalue
> 
> 
> -- 
> 
> http://dannyayers.com

-- 
Yoshio FUKUSHIGE <fukushige.yoshio@jp.panasonic.com>
Network Development Center,
Matsushita Electric Industrial Co., Ltd.

Received on Tuesday, 3 October 2006 02:52:07 UTC