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

Christoph LANGE ch.lange at jacobs-university.de
Sun Feb 22 16:49:18 CET 2009

```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).
> (a) Somehow, we need to connect the bizarre strings mph (and to a lesser
> extent kmph) with their semantic content.
> (*) I say bizarre in that 'm' is normally the abbreviation for metres, not
> miles, and only crops up here (and, though we hadn't coded it, in 'mpg'=
> "miles per gallon", for fuel efficiency). The point is that these strings
> are not partof a general pattern: one can't use 'p' as a symbol for
> division in general.
> (b) Therefore there needs to be a semantic concept on which to hook this
> parse.
> (c) It would be better if this were a well-defined concept (an OMS in this
> case), rather than a compound object.
> 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
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 additional benefit of this approach is, as I believe, the one can use
> > context-dependent presentation.  Think of kilometres per hour, which are
> > rendered as "kph" in English but as "km/h" in other languages.  (Is that
> > right?)
>
> I normally use 'kmph', but I'm not sure how general that is. Next time I
> wander outside here (i.e. Canada) I'll look more carefully at the road
> signs.

I just thought I remembered kph from car speedometers; not sure about the

Cheers,

Christoph

--
Christoph Lange, Jacobs Univ. Bremen, http://kwarc.info/clange, Skype duke4701

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