The Ontology of units of Measure (OM) 2.0 models concepts and relations important to scientific research. It has a strong focus on units, quantities, measurements, and dimensions. OM is modelled in OWL 2 - Web Ontology Language.
Base URI: http://www.ontology-of-units-of-measure.org/resource/om-2/
Namespace Prefix: om
- Ontology of units of Measure
- RecordTable ontology
- Software
- Previous versions
- Acknowledgements
- Papers on OM
The OM ontology provides classes, instances, and properties that represent the different concepts used for defining and using measures and units. It includes, for instance, common units such as the SI units metre (om:metre
) and kilogram (om:kilogram
), but also units from other systems of units such as the mile (om:mile
) or nautical mile (om:nauticalMile-International
). For many application areas it includes more specific units and quantities, such as the unit of the Hubble constant: km/s/Mpc om:kilometrePerSecond-TimePerMegaparsec
, or the quantity vaselife om:VaseLife
.
The following application areas are supported by OM:
- Geometry
- Mechanics
- Thermodynamics
- Electromagnetism
- Fluid mechanics
- Chemical physics
- Photometry
- Radiometry and Radiobiology
- Nuclear physics
- Astronomy and Astrophysics
- Cosmology
- Earth science
- Meteorology
- Material science
- Microbiology
- Economics
- Information technology
- Typography
- Shipping
- Food engineering
- Post-harvest technology
- Dynamics of texture and taste
- Packaging
Figure 1. The UML diagram below shows the class structure of the OM ontology.
The following triples express, for example, the diameter of an apple:
ex:_10Centimetres rdf:type om:Measure ;
om:hasNumericalValue "10"^^xsd:double ;
om:hasUnit om:centimeter .
ex:diameterOfApple1 om:hasValue ex:_10Centimetres ;
a om:Diameter ;
om:hasPhenomenon ex:apple1 .
ex:apple1 rdf:type ex:Apple .
where ex
is a prefixes for another namespace.
The RDF structure for this example shows as follows:
Figure 2. An RDF diagram representing the size of an apple as 10 cm.
Please not that:
In OM, scales, such as the temperature scale are handled differently than their corresponding units. For instance a temperature difference will be expressed as a measure with a unit such as °C or K, where 28°C = 28 K. On the other hand an absolute temperature of 28°C is being referred to the Celsius scale and is equal to 301 K. Usually, the scale is used. Here is an example of using a temperature scale.
OM is based on several official paper standards, such as: The Guide for the Use of the International System of Units, by the NIST.
Included in the OM repository is the RecordTable vocabulary for semantically modelling tabular data, as a supplement to the existing RDF Data Cube standard. RDF Record Table has a nested structure of records that contain self-describing observations, and is able to cope with irregular, missing and unexpected data. This allows it to escape the constraints of RDF Data Cube and to model complex data, such as that occurring in science and engineering.
As an example, consider the following Table 1. and Figure 3.
Table 1. An example table, parts of which are depicted as a RecordTable graph in Figure 3. The highlighted cells are depicted in the graph.
Figure 3. An RDF diagram representing an example using RecordTable.
Several libs support the use of OM:
om-java-libs
: A software library written in Java that uses OM to convert between units.om-phyton-libs
: Same in Phyton.
Previous versions were published on the wurvoc platform.
We would like to thank Jan Martin Keil and Sirko Schindler of the University of Jena for reviewing OM (see Unit Ontology Review and publication).
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