Re: [xml-dev] ANN: a portable data component -- length

[rjelliffe <rjelliffe@allette.com.au>]

> On 10/04/2011 06:23, Toby Considine wrote:
>> Interesting question, and one that goes to the heart of some of my 
>> current
>> obsessions...
>>
>> Is there a standard XSD of SI units for inclusion somewhere on the 
>> web

>> Is there a standard XSD of SI scale ( peta / tera / giga / mega/ 
>> ...) for
>> inclusion anywhere on the web?

 
 You are probably aware of the W3C note "Units in MathML"
 http://www.w3.org/TR/mathml-units/

 This takes the route of assigning URLs to all the concepts.

 The publishing industry (and perhaps other printing/manufacturing 
 industries) have two particular requirements that may not be obvious. 
 These are:

 1) Most people use metric, some quaint countries use imperial, and some 
 other countries may have their own native measures (such as the Japanese 
 Q?).   So rather than issues of absolute precision in measurements, it 
 is needed to have some system of units in which allows exact 
 inter-conversions: i.e. converting between inches and cm repeatedly will 
 cause any accumulated round-off errors.  (TeX, Adobe and Microsoft all 
 have their own versions of these. These are standardized in ISO PDF and 
 ISO OOXML, and I think ISO ODF uses Adobe's system.)

 2) Some interfaces allow users to enter numbers like  1/3". So the 
 metrical base described above has to cope with exact representations of 
 these as well. i.e. what base is required so that integer multiples 
 yield  1", 1cm, 1/8"i, 1/8cm, i/3", 1/3cm precisely?


 If you are wanting an exhaustive list of metrical units, include 2 
 different kinds of cubits, ISO10744 HyTime had such a thing. This 
 standard is no longer current, but still may be a good reference.

 Cheers
 Rick Jelliffe