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   Re: [xml-dev] Round 2: Identifying Data for Interchange

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Hi Don,

Don Bate wrote:
> You've got this backward. Position is always derived from distance,
> azimuth, or elevation measurements and there may not be enough
> measurements to calculate position. 

Thanks for your observations. I am sure that you are correct, but I'd
rather not go on a tangent about peculiarities of my example.  Let's
make it simpler:

Let's take a sheet of graph paper.  Put a dot on the paper.  That's the
ground station.  Now put another dot somewhere else.  That's the
aircraft.  Now calculate (derive) the distance using Pythagorean's

Now move the aircraft to another x, y location.  Calculate (derive) the
distance.  If a client were to receive a sequence of these x,y
coordinate values then he/she could:
   - calculate the distance
   - calculate the heading
   - calculate the relative location of another aircraft
   - plot this onto a map

Let me call the position data fundamental, and the distance data


Now let's get back to the hard issues:

   - should there be 2 schemas, one for fundamental data and one
     for derived data?  I will argue that there should only be
     one schema - the fundamental data schema.  Derived data is
     transient and should not have its own schema.  What do you 

   - at what point does sharing of fundamental data become a
     Service of derived data?



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