Basic units in XML (Was: Re: [QUANTITY] Units)

[Brian Thomas]

On Wednesday 21 May 2003 03:25 pm, Jonathan McDowell wrote:
> Brian,
>  My take is that the worst thing to do is specify a particular basic set.
> I may want to revert to my theorist childhood and only have one basic unit,
> the GeV, which everything else is expressed in turns of. Or I may prefer
> (Msun, AU, yr) instead of (kg, m, s). So the trick is to *support* the
> concept of a basic set, not to pick what that basic set is.


	I guess I disagree. I think to build a working  system, some choice needs to
	 be made in order for the computer to evaluate whether or not Msun is like kg.  
	Evaluation may  entail either a "equivalency" (are all units on equal footing, in
	other words, are these two things "mass"?) or "exact" (does this unit exactly
	equate to this other unit).

	For example, "gm" and "kg" are "equvalent" whereas "kg" and "1000 * gm" 
	are "exact". I dont see how you can get exactness without allowing for translation 
	of your units-to-be-compared into some basic standard.

				=b.t.


	

>   Jonathan