VOUnits: _another_ version, based on implementation feedback

[Norman Gray]

Greetings, all.

Markus has been hard at work, and has produced a parallel implementation of the VOUnits specification.  In the course of this, he has identified some ambiguities in the document and infelicities in the associated grammars.

I've made corresponding fixes to both.  The changenotes section is below, and you can inspect the changes at <https://code.google.com/p/volute/source/detail?r=2312> and <https://bitbucket.org/nxg/unity/commits/all>.

See <http://www.astro.gla.ac.uk/users/norman/temp/PR-VOUnits-1.0-20131025.pdf>

I'm as keen as anyone else to see this PR finished, but ... can you take a look and see if you object to anything.

Markus has a couple of other suggestions or issues which I didn't feel able to take an independent decision on; I'll let him raise those if he feels so inclined.

Have a good weekend.  All the best,

Norman






\item 1.0-20131025:
\begin{itemize}
\item Grammar changes: The `\%' character is now treated as a special
    case, rather than being a permitted 'STRING' character; it's only
    the CDS syntax that permits this character.  Some readability
    adjustments to the grammars.  Unit strings with leading slashes
    (eg \unit{/m3}) are no longer supported in the VOUnits syntax.
    The grammars now match Unity v0.10.
\item Changed discussion/rationale for forbidding non-ASCII
    characters.
\item Clarified that `?' -- which is specified as indicating an
    unknown unit -- is not part of the VOUnits grammar, and should be
    spotted by a caller before parsing begins.
\item Clarified the extra terminals which some grammars use.
\item Clarified that the ambiguity in \unit{dadu} should remain
    unresolved, and the correct behaviour unspecified (is it
    deci-\texttt{adu} or deka-\texttt{du}?).
\end{itemize}


-- 
Norman Gray  :  http://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK