Re: units in MathML

[was: Re: some proposals on MathML]

To reply just to your "units=" proposal:

At 3:35 PM 1/28/98, Andreas Strotmann wrote:
> - may I propose a "units=" attribute for the <cn> and <ci> elements
>  or some other mechanism for specifying units (physical, monetary, 
>  or otherwise)? 
>  In high school textbooks you will often find questions that give
>  numbers in terms of certain units, and not all numbers in the same
>  units either (e.g. a geometry question may involve the lenght of
>  the thumb and the distance between eye and thumb in inches, give the
>  height of an object at a distance in feet, and ask for the distance to
>  that object in miles).
>  Possible values of the units attribute may or may not be included in
>  the MathML definition, but the list should definitely be extensible.
>  It may be better to do this by introducing a qualifier element <unit>
>  instead that <cn> and <ci> may take, or by introducing a general
>  purpose <unit> element whose first argument would represent the
>  quantity and whose first element would represent the unit expression 
>  (km/sec^2, say, in MathML markup).
>  This would greatly improve the utility of MathML in the rest of the
>  sciences, and even more outside the sciences, I would think.  

I fully agree that support for quantities with units is desirable.

But I think we already support this, merely by allowing expressions
consisting of products of numbers and identifiers. For example,
the quantity 9.8 meter/(second ^ 2) could be expressed directly as the
MathML markup corresponding to that expression, 9.8 meter/(second ^ 2),
using identifiers such as <ci>meter</ci>.

If <ci>meter</ci> is not thought to be sufficiently unambiguous,
then I'd suggest using the definition attribute on <ci>
to make it unambiguous. (I don't know whether this attribute
was present in the Jan 6 version of the draft. It will permit
marking certain MathML expressions with a "definition" attribute,
whose format is not specified except that it can be a URL; this is
enough to allow someone owning a certain domain name to establish a
convention that expressions marked with definitions which are URLs
in that domain mean what that someone says they mean.)

(I concentrate on Chapter 3, so I don't know for sure that <ci>
accepts the definition attribute, but I would guess and hope it does.)

- Bruce Smith