Established vocabularies for units in RDF?

I am wondering today what is the state of the art in terms of representing
measurement units in RDF.  I break this down into four layers:

(1) Measurement units regarded as basic,  such as "meter",  "degree
centigrade"
(2) Measurement units in the abstract such as "length",  "time"
(3) Measurement units created by the composition of basic units
("meters"/"seconds")
(4) So far we are representing measurement units in and of themselves,  but
(4) would including associating measurement units with properties in a
schema and/or specific instance values.

What is out there to address this at the various levels?

-- 
Paul Houle

*Applying Schemas for Natural Language Processing, Distributed Systems,
Classification and Text Mining and Data Lakes*

(607) 539 6254    paul.houle on Skype   ontology2@gmail.com

:BaseKB -- Query Freebase Data With SPARQL
http://basekb.com/gold/

Legal Entity Identifier Lookup
https://legalentityidentifier.info/lei/lookup/
<http://legalentityidentifier.info/lei/lookup/>

Join our Data Lakes group on LinkedIn
https://www.linkedin.com/grp/home?gid=8267275