[QUANTITY] Why quantities always have errors (Was: Re: [QUANTIT] Use-cases, role in larger scheme)

[Brian Thomas]

On Monday 17 November 2003 03:21 pm, Martin Hill wrote:
> >    I believe that quantities are framed by their *usage*, not their
> > *origin*. IF we need to have a universal atom that we can pass around,
> > clip apart/rebuild, and search for, then we don't care if something is a
> > measurement, or a simulation or not. We need to lump all of the types of
> > error together in the interface in order to be able to compare, clip,
> > paste, parts which are measured, defined, calculated values.
>
> I think that's rather the point - there doesn't appear to be a universal
> atom to pass around.  Not one that you would want to compare/etc blindly
> with any other.  Any universal operations (clone, clip, paste, store,
> etc) are based on a much higher abstract class (eg 'Object' in java) or
> similarly high level/simple interfaces.

	I think you read to obliquely into my statements. I was speaking of 
	the need to appropriately cut, paste, sort quantities. Cut n paste of
	any old object is not adequate. We need to do these things appropriately
	(and in a scientific manner) for numbers (and I would add, strings)
	as well. 

	Granted all objects and quantities have values, but the similarity ends
	there. Quantities hold things which need (if we are to be scientific) values with
	units and some type of accuracy. Even in the cases where these dont
	appear to be needed, they actually are, and are implied (as per my reponse
	to Pat about the parabola). 

>
> >    Having separate classes for measurement, calculation, simulation
> > quantities doesn't get you much (or anything).
>
> These are sources of values rather than types (classes) of values...?
>
> I think having distinct types is actually quite useful, as you can be
> sure you're comparing only things that are sensible to compare - the
> sensibleness being defined by those particular classes. 

	This might be true if you never compare measurements with calculations,
	or simulations with calculations or so on. But that isnt the case, is it? 

	We have a very real need to compare measurements with calculations or with 
	"declared values" (such as a theorist defining the speed of light to be "1").

	Give me a use-case or two where you need to limit the use of the quantity
	by it origin AND how that would change the calculation (or a cut, paste op).

	Cheers,

	-=b.t.


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  * Dr. Brian Thomas 

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