How would you express the concept of a given measure to be 3 meters ? Is there an ontology for units ?
There's also this work-in-progress draft: QUDT - Quantities, Units, Dimensions and Data Types in OWL and XML.
This document is currently "Work in Progress" and will be improved incrementally during the fall of 2009.
The Measurement Unit Ontology has extensive discussion of various possible patterns and an ontology.
A quick search on SchemaWeb turned up units.owl and unitsInstances.owl, parts of a science ontology.
I can’t readily find a property for connecting a measurement to a unit, but I think it ought to be there as well.
As for the way to express it, here’s an example from the RDF Primer:
exproduct:item10245 exterms:weight _:weight10245 .
_:weight10245 rdf:value "2.4"^^xsd:decimal .
_:weight10245 exterms:units exunits:kilograms .
I just found a pretty decent ontology description, and I think it actually does the job quite well...
The Open Biomedical Ontologies also has an suitable ontology for units:
http://www.obofoundry.org/cgi-bin/detail.cgi?id=unit
The question is, are all mentioned unit ontologies compatible?