Units of measurement?

[Marcelo Cantos]

Kay Michael wrote:

> > my approach is to have an attribute for the value in a fixed
> > SI unit...  So for speed it would be something like
> >
> > He was travelling at <Velocity value="1">3600 kph</Velocity>
> >
> Surely the SI unit of velocity is metres per second? And the correct
> abbreviation is ms<sup>-1</sup>? [how do you put that in an attribute?]

Actually km _is_ an SI unit (multipliers are part of the SI).  I also believe
hr is (though I can't claim this with the same degree of certainty).  It is also
permissible to use the division symbol '/', so:

  km/hr

is perfectly reasonable.  kph, on the other hand, most certainly isn't SI.

Furthermore, ms<sup>-1</sup> represents the unit 'milliseconds to the
minus -1', hence the SI requirement to insert either spaces between unit
components or, preferably, a dot:

  m.s<sup>-1</sup>

As for their use in attributes, I seem to remember reading that the power
notation is never required.  It only keeps things tidy.  It really depends
on whether you are concerned to represent the format or the semantics,
though if formatting is the goal then I'd say it doesn't really belong in an
attribute anyway.


Cheers,
Marcelo



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