QUDT

QUDT, short for Quantities, Units, and Dimensions, is an ontology and data model for representing physical quantities, their units, and their dimensions in the semantic web. It provides a formal vocabulary to describe what is being measured, the units used to express the measurement, and the dimensional relationships among quantities, enabling interoperable data integration across disciplines such as science, engineering, and the Internet of Things.

The QUDT model centers on core concepts such as QuantityKind, Unit, and Dimension. QuantityKind represents the type of quantity (for example length, mass, time). Unit denotes a specific measurement unit (such as meter, kilogram, second), often with references to canonical or SI units. Dimension captures the dimensional analysis associated with a quantity (for instance L for length, M for mass). The vocabulary also defines relationships and properties that link these concepts, including how a quantity can be expressed in a particular unit and how units convert to one another via scale factors or offsets.

QUDT is implemented as RDF/OWL vocabularies and provides machine-readable URIs for quantities and units, along with conversion information to support unit normalization and dimensional consistency. It also aligns with established standards such as the SI system and UCUM for unit representation.

Applications of QUDT include data integration in knowledge graphs, scientific data repositories, and engineering dashboards, where consistent interpretation of measurements and automatic unit conversions are important. The project is typically maintained as an open vocabulary, with documentation and downloadable ontology files for use in semantic technologies.