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RE: What are units-of-measure? e.g., what's a "kilometer"?

• To: "Roger L. Costello" <costello@m...>, xml-dev@l...
• Subject: RE: What are units-of-measure? e.g., what's a "kilometer"?
• From: Allen Razdow <arazdow@m...>
• Date: Thu, 17 Jul 2003 12:11:11 -0400

Hi Folks,

Dimensional analysis and theory behind it is a deep subject.  Mathsoft is
working on an XML ontology for practical units.  See also work at NIST:

http://unitsml.nist.gov

The high-level class would be something like "physical quantity" or
"quantity of measure", which has attributes of "scalar value" and some
combination of "dimension" and "units".  Dimension (like "ENERGY" isn't
enough unless you specify a "dimensional system" like SI or CGS.  In CGS,
gm*cm^2*sec^-2 is a unit-cluster representing the dimension="CGS:energy".

I'm not sure I see the point of the functional view.  I rather see the
function as property(physical object) as in length(object).  Dimension and
units are a property of the type returned by this function, which is
"quantity of measure".

-Allen

-----Original Message-----
From: Roger L. Costello [mailto:costello@m...] 
Sent: Thursday, July 17, 2003 9:48 AM
To: xml-dev@l...
Cc: Costello,Roger L.

John Cowan wrote:

> > 2. Is kilometer a function? e.g., kilometer(Yangtze) --> 6300
> >    In general: kilometer(physical object) --> number
> >    "The kilometer function maps a physical object to a number."
>
> I think this view is the most nearly correct, but it needs amplification:
> it doesn't capture that it's the *length* (rather than, say, the
> average depth) of the Yangzi that is 6300 km.  So we can rewrite it
> in terms of relations as follows:
>
> Yangzi length X
> X kilometer 6300
>
> where "kilometer" is a relation that maps a length (an abstract property
> of a physical object) into a pure number.

So, kilometer is a function of this sort:

   kilometer(length(Yangtze)) --> 6300

"kilometer is a function which maps the length of the Yangtze to 6300."

Another example:

   kilometer(avg-depth(Yangtze)) --> 0.25

"kilometer is a function which maps the average depth of the Yangtze to
0.25."

The general case is:

   kilometer(distance) --> number

where distance is an abstract dimension object.

How are functions represented syntactically in XML?  Given the above
viewpoint, this form no longer seems appropriate:

    <River id="Yangtze">
          <length units="kilometer">6300</length>
    </River

Perhaps a more faithful representation of:

    kilometer(length(Yangtze)) --> 6300

is this:

    <River id="Yangtze">
          <length>
                <kilometer>6300</kilometer>
          </length>
    </River>

Thoughts?  /Roger



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