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Problems with MUO units ontology

From: Tim Berners-Lee <timbl@w3.org>
Date: Sat, 4 Jul 2009 11:03:48 -0400
Message-Id: <2EB0764F-7E45-4ED4-88CB-0D6500E936D4@w3.org>
To: sergio.fernandez@fundacionctic.org, luis.polo@fundacionctic.org
Cc: www-archive@w3.org, Dan Connolly <connolly@w3.org>, Ivan Herman <ivan@w3.org>
Diego and Luis,

I am concerned that the MUO ontology you are proposing people adopt  
has serious issues.  I was reading

http://forge.morfeo-project.org/wiki_en/index.php/Units_of_measurement_ontology#Alternatives_to_represent_measurable_quantities_in_RDF


You refer to my Design Issues note on Interpretation properties but  
you don't seem to have taken it into account.

You say, (I add the <> brackets you forgot from the N3 in the article)


:Spain :area [
            muo:numericalValue "504782"^^xsd:double ;
            muo:measuredIn :Sq_Km
            ] ;
        :area [
            muo:numericalValue "194897"^^xsd:double ;
            muo:measuredIn :Sq_Miles
            ] .

But I would expect Spain to have, in principle, just one area. I would  
expect :area to be a functional property.   If Spain has one area,  
then we get the confusion:


:Spain :area [
            muo:numericalValue "504782"^^xsd:double ;
            muo:measuredIn :Sq_Km;
            muo:numericalValue "194897"^^xsd:double ;
            muo:measuredIn <Sq_Miles>
            ] .

which is completely muddled an ambiguous of course.

I suppose you can avoid this using the extra arc as in

:Spain :area [
     muo:expressableAs [
            muo:numericalValue "504782"^^xsd:double ;
            muo:measuredIn :Sq_Km
            ] ;
    muo:expressableAs [
            muo:numericalValue "194897"^^xsd:double ;
            muo:measuredIn #Sq_Miles
            ] .

but that is cumbersome.

By contrast, the Interpretation Properties pattern, which you do not  
review in your article at all, makes it much simpler.


:Spain   :area  [ :Sq_Km  "504782"^^xsd:double].


By the way, in N3 you can write the above as

:Spain   :area  [ :Sq_Km  504782e0].

or even

:Spain   :area  504782e0^:Sq_Km.

This does not have the problem above, as there is no issue with

:Spain   :area  504782e0^:Sq_Km ,  194897e0^:Sq_Miles .

that is

     :Spain     :area  [ :Sq_Km 504782.0e+00 ];
                    :area [ :Sq_Miles 194897.0e+00 ] .

as the same area can be expressed using two different units.
Could you convert the MUO work to use interpretation properties?

Tim BL
Received on Saturday, 4 July 2009 15:04:27 GMT

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