Describing the relationships between units-of-measure?

["Roger L. Costello" <costello@mitre.org>]

Hi Folks,

Let's suppose that units-of-measure are represented as properties, e.g,

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

Here is an example where the length of the Yangtze River is described
using a mile property:

   <River id="Yangtze">
        <length>
            <mile>3914</mile>
        </length>
   </River>

It would be very useful to be able to state the relationship between the
kilometer and mile properties.  For example, suppose that I wish to
define the kilometer property:

    <Property id="kilometer">
        ...
    </Property>

When I define this property it would be very useful to express that this
property is related to the mile property, e.g.,

    <Property id="kilometer">
        "This property is related to the mile property.  Namely,
         if the value of a mile property is multiplied by 1.62 
         and it yields a value that is equal to the value of this
         property, then the two properties are said to represent
         the same distance."
    </Property>

Do you have any suggestions on how to syntactically represent this
relationship statement? 

Here is a more complex example, showing a map location using two
different coordinate systems:

<Map id="M1">
    <location>
        <cartesian-coordinate>
            <x>
                <kilometer>100</kilometer>
            </x>
            <y>
                <kilometer>100</kilometer>
            </y>
        </cartesian-coordinate>
    </location>
</Map>

<Map id="M21">
    <location>
        <polar-coordinate>
            <r>
                <kilometer>141.421</kilometer>
            </r>
            <theta>
                <radian>0.7341</radian>
            </theta>
        </polar-coordinate>
    </location>
</Map> 

It would be very useful to be able to state the relationship between
these coordinate systems, e.g.,

    <Property id="cartesian-coordinate">
        "This property is related to the polar-coordinate 
         property.  Namely, if these equations are satisfied:
             x = r sin theta
             y = r cos theta 
         then the two properties are said to represent the same
         location."
    </Property>

(For the moment let's ignore the conditions that Alaric noted yesterday)

Do you have any suggestions on how to syntactically represent this
relationship? 

/Roger