[SUMMARY] QuantitativeValue / Units of Measure - Proposal

I went through the schemas and found the uses of
http://schema.org/QuantitativeValue:

Time Duration:

http://schema.org/advanceBookingRequirement
http://schema.org/deliveryLeadTime
http://schema.org/durationOfWarranty
http://schema.org/eligibleDuration

Dimensions / weight

http://schema.org/depth
http://schema.org/height
http://schema.org/weight
http://schema.org/width

Counts (possibly unit less?)

http://schema.org/eligibleQuantity
http://schema.org/inventoryLevel

Having some familiarity with the UN/CEFACT efforts, I also went through
their unit codes and I find them troubling for general use:

  1. XML Schema's durations aren't possible.  A great deal of effort went
into making a value space and lexical representation that is based on ISO
time standards (ISO 8601).

  2. The codes are odd for common use (e.g. Hour = HUR, instead of 'H' or
'h', ANN = year, instead of 'yr' or 'Y', GRM = gram, instead of 'g')

  3. There are very general properties of depth, heigh, width, and weight
for which I could expect to use outside of UN/CEFACT contexts.

That said, I do think it makes sense to have a "unit code" property for
contexts where UN/CEFACT information is being described.  That property
should never be used for other purposes because of the broad nature of
these codes and the fact that a random two or three letter code could mean
something (e.g. 11 = outfit).

On the other hand, if I want to describe the weight of an object using SI
units, I need a way to say that with a different property.  That is, I
should be able to use the standard prefixing scheme of SI units to say
"kg", "g" "mg" and so on without having to resort to looking up a strange
code.

If you look at Wikipedia's entry on SI units [1] or  QUDT [2], you'll see
the consistent terminology for a unit abbreviation is "symbol".  Since we
have one namespace, "symbol" alone has far too many interpretations and so
"unitSymbol" might be better.

As mentioned before, grounding a unit by some well defined concept is a
really good idea and URI is seems the best option because it will integrate
well with QUDT.

Proposal:

Add two properties to QuantitativeValue: one for the unit symbol and one
for the unit's "reference URI":

    http://schema.org/unitSymbol - the unit symbol, a string value
    http://schema.org/unit - the URI of the unit's definition (e.g. QUDT
unit:Gram, expanded)

and this allows:

    <p typeof="QuantitativeValue">
        <span property="value">10</span><span property="unitSymbol">g</span>
    </p>

and alternatively, for more specificity:

    <p property="weight" typeof="QuantitativeValue">
        <span property="value">10</span><span
property="unitSymbol">g</span><span property="unit" resource="unit:Gram"/>
    </p>

or

   <p property="weight" typeof="QuantitativeValue">
       <span property="value">10</span><span property="unitSymbol"><span
property="unit" resource="unit:Gram">g</span></span>
   </p>

[1] http://en.wikipedia.org/wiki/International_System_of_Units
[2] http://www.qudt.org/

-- 
--Alex Milowski
"The excellence of grammar as a guide is proportional to the paucity of the
inflexions, i.e. to the degree of analysis effected by the language
considered."

Bertrand Russell in a footnote of Principles of Mathematics