UoM_Ontology_Standard OWL - draft

Editor: Rob Raskin, Chip Masters and HansPeter_de_Koning

... placeholder for the UoM_Ontology_Standard OWL drafting work

SysML QUDV Ontology

Editor: HansPeter_De_Koning

The input from the SysML QUDV (Quantities, Units, Dimesions and Values) ontology in OWL2 DL can be found at http://www.omgwiki.org/OMGSysML/doku.php?id=sysml-qudv:qudv_owl .

The ontology is split into two main modules:

• A base ontology SysML-QUDV that defines all classes and properties
• The ISQ and SI individuals ontology SysML-QUDV-SI for the International System of Quantities and the International System of Units (i.e. finally should cover all of ISO/IEC 80000)

It would be a natural extension to add a third module that defines the most used non-SI units (with conversion factors) from SP811 "NIST Guide to the SI" Appendix B. Conversion Factors.

The main concepts (classes) in QUDV that correspond closely to VIM and that are probably also applicable to QUOMOS are:

• [[SystemOfQuantities]]
• QuantityKind or [[KindOfQuantity]], an abstract superclass with subclasses:
  • [[SimpleQuantityKind]]
  • [[DerivedQuantityKind]]
  • [[SpecializedQuantityKind]]
• Quantity
• Dimension or QuantityDimension
• [[SystemOfUnits]]
• Unit or [[UnitOfMeasure]], an abstract superclass with subclasses:
  • SimpleUnit
  • DerivedUnit
  • [[ConversionBasedUnit]], an abstract superclass with subclasses:
    • PrefixedUnit
    • [[LinearConversionUnit]]
    • [[GeneralConversionUnit]]
• Prefix or [[UnitOfMeasurePrefix]]
• Scale

Remarks on current QUDV implementation

1. In QUDV, base quantities and base units are modeled as object properties of [[SystemOfQuantities]] and [[SystemOfUnits]] (i.e. roles). We distinguish between simple and base kinds of quantity and units:
   1. A simple kind of quantity or a simple unit does not depend (for its definition) on any other kind of quantity or unit.
   2. A base kind of quantity is a role that is assigned to selected kinds of quantity in the context of a system of quantities.
   3. A base unit is a role that is assigned to selected units in the context of a system of units.
2. For the SI system of units, this separation of simple and base units e.g. cleanly solves the problem of selecting the PrefixedUnit "kilogram" as a base unit. The "kilogram" is defined through object properties to the Prefix "kilo" and to the SimpleUnit "gram".
3. QUDV contains an algorithm written in OCL that precisely specifies how a quantity dimension for a given kind of quantity in a given system of quantities can be derived automatically.
4. In the OWL version of QUDV the [[AffineConversionUnit]] (conversion unit defined with factor and offset to a reference unit) is removed because this is better handled by a [[LinearConversionUnit]] and adding an equivalent property between scale value definitions of different scales. E.g. the offset needed to convert between a thermodynamic temperature in kelvin and a Celsius temperature in degree Celsius can be derived when the triple point of water scale value definitions in both the Kelvin and Celsius scales are declared equivalent.
5. The [[SpecializedQuantityKind]] is modeled explicitly because QUDV complies with the strict separation into (MOF) meta levels in UML. QUDV is a pure level M0 UML or SysML <<modelLibrary>>. Accordingly in OWL2 DL it is not allowed to use metaclasses (using owl:class). This is also not supported in Protégé v4 (yet). In OWL2 Full it would perhaps be possible to model the kind of quantity / quantity specialization relationships more elegantly.