Using 223 with QUDT

Because this standard includes references to measurements of physical properties, it is necessary to provide a model representation of units of measure as well as what those units are quantifying (e.g. temperature, power, etc.). This standard builds upon the “Quantities, Units, Dimensions and Types” (QUDT) ontology which is the leading open-source model of units and related concepts expressed in RDF/SHACL. The QUDT model is documented at the QUDT website. The key concepts used here are the classes Unit and QuantityKind. The 223 standard is compatible with Version 2.1.41 of QUDT and is expected to be compatible with all newer versions as well.

If a user wants control over which version of QUDT is used, they can download any specific version at the QUDT Github Release page for use within their application. This is the recommended method because it ensures nothing changes without the knowledge of the user. Alternatively, one can dynamically load the QUDT graphs into an application from the internet via the graph URIs identified in the import statements of the 223 standard, such as http://qudt.org/2.1/vocab/unit. This approach will always load the latest version of QUDT, but note that this approach loads the OWL schema for QUDT rather than the SHACL schema. As described in the Protege Users instructions, the imports specified in the “facade” file that is resolvable on the web (http://qudt.org/2.1/schema/facade/qudt) is configured to load the OWL schema rather than the SHACL schema. To use the SHACL schema in the dynamic loading method, a local copy of the facade file must be downloaded first and edited as follows:

Change this line:
  owl:imports <http://qudt.org/2.1/schema/qudt> ;  
To:
  owl:imports <http://qudt.org/2.1/schema/shacl/qudt> ;

A useful resource for the modeler is the QUDT catalog found here, where all the units, quantity kinds and other concepts are listed. Each concept is fully dereferenceable, so for example, the Ampere has the URI http://qudt.org/vocab/unit/A. Using content negotiation, this link resolves to an HTML page for a human reader, and to interpretable code for a machine.