Re: [unitsml] Suggested Schema Changes

["Martin S. Weber" <martin.weber@nist.gov>]

Linstrom, Peter wrote:
> All,
> 
>    Here's a quick response to Martin's two points.
> 
> 1.) "Hectare" and "are" are included as separate enumerated
>     root units because they are generally treated as separate
>     units. For example "Hectare" is approved for use with the
>     SI, while "are" is not. I believe the "centihectare" is
>     used in some eastern European real estate documents. I
>     know this all seems to defy logic, but so does much of
>     human endeavor.

ok

> 
> 2.) In SP 811, two expressions are provided for derived units,
>     one with based on other derived units and one solely with base
>     units. I think the former would be preferable to the latter
>     (since the latter can be obtained from the former). If this
>     convention is followed, I don't see the need for multiple
>     "RootUnits" elements. I think the value of allowing multiple
>     combinations of units is outweighed by the risk of having two
>     incompatible "RootUnits" elements.

As I've written in the case of watt; an electrical engineer might think of it 
as volt-ampere. Other physicists rather as Joule per second. I see the danger 
of specifying conflicting information, too, but then again we do not check 
whether e.g. dimensions given (via a dimensionUrl) of a unit also agree with 
the referred to root units.
[also in the light of unitsdb -- if we want to offer multiple view on things, 
we *need* to be able to return multiple RootUnits].
I think we should discuss this further on the meeting.

-Martin