- From: Yoshio FUKUSHIGE <fukushige.yoshio@jp.panasonic.com>
- Date: Tue, 03 Oct 2006 11:52:29 +0900
- To: semantic-web@w3.org
- Cc: fukushige.yoshio@jp.panasonic.com, Tim Berners-Lee <timbl@w3.org>, "Elisa F. Kendall" <ekendall@sandsoft.com>, Robert Dodier <robert.dodier@gmail.com>, Evan Wallace <ewallace@cme.nist.gov>, Danny Ayers <danny.ayers@gmail.com>
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