Units of Measure
One unit dictionary, two layers. Energistics UoM — the standard shared with OSDU and Open Footprint — is the system of record; QUDT gives the same units an RDF face in the knowledge graph.
Why Two Layers
Emissions math lives or dies on unit conversion, so the conversion authority must be the same dictionary OSDU and Open Footprint already use: Energistics UoM. But a dictionary can't answer SPARQL queries. QUDT is the RDF face of those same units — and because every QUDT unit carries crosswalks to UCUM, UNECE, IEC 61360, OM, and the BIPM SI Digital Framework, one alignment buys interoperability with six unit systems. A thin Energistics-to-QUDT crosswalk connects the layers.
The Two Layers
Energistics Unit of Measure
ImplementedSystem of record — dictionary & conversion authority
- ~200 quantity classes, 2,000+ units with normative conversion factors
- The unit dictionary behind OSDU's Frame-of-Reference unit service
- Referenced by Open Footprint common entities — one dictionary across the platform
- Stable custodianship under The Open Group since 2022
QUDT
In DevelopmentSemantic layer — the RDF face of the same units
- Actively maintained units ontology with ~monthly releases
- Per-unit crosswalks: UCUM, UNECE, IEC 61360, OM, BIPM SI Digital Framework
- The standard units vocabulary for SOSA observations in the knowledge graph
- W3C-member nonprofit governance
The Crosswalk
Example:
t/a → unit:TON_Metric-PER-YR → ucum: t/aTonnes per annum in the Energistics dictionary, as a QUDT IRI in the knowledge graph, with standard codes for every downstream consumer.
The crosswalk covers the quantity classes the platform actually uses — emissions, energy, flow, and concentration — and grows with the model, never as a big-bang migration of all 2,000+ units.
Part of the ontology layer
QUDT is one of five alignment ontologies extending the Sustainability Ontology.