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Michael Hucka wrote:
> To cope with this, we are tentatively thinking of using the
> following set of guidelines:
>
> 1) If the number is the only thing contained inside a <math>
> (such as the original example involving a delay on
> Events), assume that the units of the number are the
> units defined for that field (so, timeUnits for delays).
>
> 2) In all other cases, assume pure numbers have no units.
>
> This handles the first case, and also addresses the second
> case. (In the second case, there would be a unit validation
> failure because the "2" would not have units and therefore
> the overall expression could not have consistent units.)
>
Well, this isn't really too bad. In many formula (especially
empirically defined), there are numbers with units put in to make the
units work. Numbers could be assumed to be dimensionless, and people
could be required to use unit-fixing factors.

One other solution could be to add a mathUnits attribute to the element
containing the math. The mathUnits could be assumed to be treated like
the number 1 with mathUnits multiplied by any units used by any other
variables. I.e. for your example:

<stoichiometryMath mathUnits="metre">
<math xmlns="http://www.w3.org/1998/Math/MathML">
<apply>
<plus/>
<ci> S </ci>
<cn> 2 </cn>
</apply>
</math>
</stoichiometryMath>

The units for the math expression would be metre*(the units of S).

Have a good day,

Bill
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