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Re: (Round 2) Proposed Extensions to OWL

From: Richard H. McCullough <rhm@cdepot.net>
Date: Mon, 7 Jul 2003 07:18:15 -0700
Message-ID: <000d01c34492$afa95510$bd7ba8c0@rhm8200>
To: "Thomas B. Passin" <tpassin@comcast.net>
Cc: "Roger L. Costello" <costello@mitre.org>, <www-rdf-interest@w3.org>

I agree.
I should have said that the value of the measurement
of a physical quantity is a literal number.

Dick McCullough
knowledge := man do identify od existent done;
knowledge haspart proposition list;

----- Original Message ----- 
From: "Thomas B. Passin" <tpassin@comcast.net>
To: "Roger L. Costello" <costello@mitre.org>; <www-rdf-interest@w3.org>
Sent: Monday, July 07, 2003 6:39 AM
Subject: Re: (Round 2) Proposed Extensions to OWL


>
> [Richard H. McCullough]
>
> > This conceptual model is OK, but unnecessarily complicated,
> > and produces RDF descriptions which are just too long.
> >
> > Since these physical quantities are just literal numbers,
> > they can be expressed as attributes of attributes, e.g.
> >     <ex:River ex:Yangtze>
> >         <ex:length units:kilometer=6300/>
> >     </ex:River>
> >
>  Well, that is just the point.  Physical quantities are __not__ just
numbers
> with units attributes.  They - or rather their measurements, which is
really
> what we are talking about here - may have sets of mesaurements, various
> units some of which may be named and some of which may be unnamed (what is
> the unit which is dimensionally kPa/m-s^1.5 ?), they have accuracy and
> precision, they have provenance, the measurements may change over time
> (after the Russians changed their standard thermometer for measure
outdoors
> temperatures in the 1920s (I think it was), all subsequent temperatures
> turned out to be inconsistent by a few degrees with data taken using the
old
> style thermometers - you have to  know when a Russian weather reading was
> taken to be able to make proper use of it).
>
> Furthermore, conceptually there can even be different kinds of things
called
> lengths, etc.  One example is the area of a rectangle vs the surface area
of
> a rectangular pice of rough cloth the with the same width and length.
Thus
> there are physical quantities, measurements of physical quantities, and
the
> values of those measurements.  The values may not even be simple numbers.
> They may be vectors or matrices, for example.
>
> Of course, it all depends on what you want to do.  Roger Costello asked
how
> to represent  an equality test to state that two lengths written in
> different units were equivalent.  You cannot assess equality unless you
know
> the units conversion formula and the precision to be used in the test,
and,
> if the two numbers represente different field measurements rather than
just
> a conversion between two units, the precision and accuracy of the
> measurements as well.
>
> The model you said is too complicated is intended to allow one to make
> statements about
>
> 1) The kind of physical quantity
> 2) A measurement of a physical quantity
> 3) The measurement value(s) of a particular measurement.
>
> Thus you need a stripe for each of the three, plus whatever you need to
> model the measurement values.
>
> But no, it is not the simplest way you could record a single number that
is
> somehow associated with the subject.
>
> Cheers,
>
> Tom P
Received on Monday, 7 July 2003 10:18:52 GMT

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