title: units of measurement in owl and rdf
body: <p>I'm creating linked data of materials and their physical properties, and I'm having trouble with setting units for certain properties. My individual material <code>:AlMg3</code> has some mechanical properties like:</p>
  
  <pre><code>:AlMg3 prop:hasTensileStrength "300" .
  :AlMg3 prop:hasYieldStrength   "2" .
  :alMg3 prop:hasDensity         "2200" .
  </code></pre>
  
  <p>How to put units for that values? My first idea was to make new datatypes, e.g.:</p>
  
  <pre><code>unit:megaPascal rdf:type   rdfs:datatype ;
                  rdfs:label "MPa" .
  
  unit:Pascal rdf:type   rdfs:datatype ;
                  rdfs:label "Pa" .
  </code></pre>
  
  <p>and then use them like this:</p>
  
  <pre><code>:AlMg3 prop:hasTensileStrength "300"^^unit:megaPascal .
  :AlMg3 prop:hasYieldStrength   "2"^^unit:Pascal .
  </code></pre>
  
  <p>Then I'd want to relate these units like this:</p>
  
  <pre><code>unit:megaPascal prop:hasBaseUnit   unit:Pascal .
  unit:pascal     prop:hasBaseSIUnit unit:kilogramPerMeterSecondSquared .
  </code></pre>
  
  <p>Is this possible? The units would be datatypes, and I can't put datatype properties between them, except for annotation properties? Is it possible to make those units individuals (or even classes) and use them like that a datatype after some value?</p>
  
  <p>I saw OWL ontologies for QUDT (Quantities, Units, Dimensions and Data Types), but I was going to try to create something simpler myself.</p>