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Re: Round 2: Identifying Data for Interchange

down jones

	Actually, I think your example is very illustrative of how 
the generalization that you propose breaks down under real-world 
engineering situations. In some situations the raw information is 
needed, sometimes the calculated information is needed, sometimes the 
raw informations is not available, and sometimes the calculated 
information is not available, and sometimes the raw information comes 
from independent sources. Sometimes the raw information is your 
protected asset, sometimes the calculated information is your 
protected asset, and sometimes the calculation itself is your 
protected asset.

	Let me use another example that gets away from the aircraft 
example: the Dow Jones Industrial Average. This is clearly a derived 
number from the fundamental data of the stock prices for the 
component stocks.  If I understand your proposed rule, the Dow 
wouldn't appear in a schema and everyone would have to know how to 
calculate the Dow. They'd also have to know which stocks comprised 
the Dow at what times so they could compute the value for historical 
purposes. This is clearly not what people currently do nor do they 
wish to do it.

	Have I misunderstood what you're proposing?

Don Bate

At 5:16 PM -0500 1/7/03, Roger L. Costello wrote:
>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
>      etc.
>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
>      think?
>    - at what point does sharing of fundamental data become a
>      Service of derived data?
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Don Bate               | Specializing in Consulting and Mentoring in
Bate Consulting, Inc   | Object-Oriented Technologies,
                        | Software Architecture, and Software Process
(972) 618-0208 voice
(972) 618-0216 fax


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