[Om] Abbreviating units [Re: Questions about representing units]

Professor James Davenport jhd at cs.bath.ac.uk
Sun Feb 22 17:02:08 CET 2009

On Sun, February 22, 2009 3:49 pm, Christoph LANGE wrote:
> On Sunday 22 February 2009 16:31:43 Professor James Davenport wrote:
>> > an explicit markup for abbreviated units would make sense, as it would
>> > facilitate parsing.  On the other hand, one could argue that this is a
>> > subproblem of the larger problem of parsing presentation markup back
>> > to content markup -- a problem that has not yet been solved
>> > sufficiently.
>> AGREED (but why make it harder by adding this). Our (Davenport/Naylor)
>> reasoning went roughtly like this (as far as I can reconstruct it).
>> Of course, you're welcome to disagree with any step of this reasoning.
> I largely agree that this is a more pragmatic solution of the problem.
> James, I think you are aware of that, but for the sake of completeness,
> allow
> me to note the following about (*): Our notation definitions do not say
> that
> "p" is an "alternative rendering" of arith1#divide, but that we render the
> complete expression (divide mile hour) as "mph".  If we had a parser for
Agreed in this direction.
> applying these notation definitions in reverse, parsing "mph" back to
> (divide
> mile hour) would still work, as long there is no other notation definition
> in the knowledge base that renders something else to "mph".
The problem is that,in the reverse direction, 'm' as a child of 'p' has to
parse as miles, whereas 'm' as a child of '/' has to parse as metres -
think of 'm/s'.

Backwards compatibility with ad-hoc ery is a pain in the neck!

James Davenport
Visiting Full Professor, University of Waterloo
Hebron & Medlock Professor of Information Technology and
Chairman, Powerful Computing WP, University of Bath
OpenMath Content Dictionary Editor
IMU Committee on Electronic Information and Communication

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