Replace 'equivalentClass' definitions of 'Unit' sublasses with 'subclass' and 'type' statements

[jmkeil]

Currently, (almost) all subclasses of unit are equivalent to a union of some prefixed unit classes and a oneOf class.

Example:

  <owl:Class rdf:about="&om;AreaUnit">
    <rdfs:label xml:lang="en">area unit</rdfs:label>
    <rdfs:subClassOf rdf:resource="&om;Unit"/>
    <owl:equivalentClass>
      <owl:Class>
        <owl:unionOf rdf:parseType="Collection">
          <owl:Class>
            <owl:oneOf rdf:parseType="Collection">
              <om:Unit rdf:about="&om;acre-International"/>
              <om:Unit rdf:about="&om;acre-USSurvey"/>
              <om:Unit rdf:about="&om;are"/>
              <om:Unit rdf:about="&om;barn"/>
              <om:Unit rdf:about="&om;circularMil"/>
              <om:UnitExponentiation rdf:about="&om;squareMetre"/>
              <om:UnitExponentiation rdf:about="&om;squareInch-International"/>
              <om:UnitExponentiation rdf:about="&om;squareFoot-International"/>
              <om:UnitExponentiation rdf:about="&om;squareYard-International"/>
              <om:UnitExponentiation rdf:about="&om;squareMile-International"/>
            </owl:oneOf>
          </owl:Class>
          <owl:Class rdf:about="&om;PrefixedAre"/>
          <owl:Class rdf:about="&om;SquarePrefixedMetre"/>
        </owl:unionOf>
      </owl:Class>
    </owl:equivalentClass>
  </owl:Class>

I propose to replace these definitions with rdf:type and rdfs:subClass statements.

Example:

  <owl:Class rdf:about="&om;AreaUnit">
    <rdfs:label xml:lang="en">area unit</rdfs:label>
    <rdfs:subClassOf rdf:resource="&om;Unit"/>
  </owl:Class>

and (in Turtle for the sake of simplicity)

om:acre-International rdf:type om:AreaUnit .
om:acre-USSurvey rdf:type om:AreaUnit .
om:are rdf:type om:AreaUnit .
om:barn rdf:type om:AreaUnit .
om:circularMil rdf:type om:AreaUnit .
om:squareMetre rdf:type om:AreaUnit .
om:squareInch-International rdf:type om:AreaUnit .
om:squareFoot-International rdf:type om:AreaUnit .
om:squareYard-International rdf:type om:AreaUnit .
om:squareMile-International rdf:type om:AreaUnit .
om:PrefixedAre rdfs:subClassOf om:AreaUnit .
om:SquarePrefixedMetre rdfs:subClassOf om:AreaUnit .

Reasons:

• The current statements are to strong, as they exclude the existence of further units. They assume OM is 100% complete and that makes reuse more difficult, as one cannot add a unit without changing OM statements (#66).
• These strong statements cause higher reasoning complexity (#79).

The required changes could probably be done with a few SPARQL UPDATE queries, given OM would uses a common serialization style (#80).