ontology is the branch of metaphysics dealing with the nature of being.
It can also mean ‘a set of concepts and categories in a subject area or domain that shows their properties and the relations between them: what’s new about our ontology is that it is created automatically from large datasets | we’re using ontologies to capture and analyse some of the knowledge in our department.’[1]
Information science
In information science an ontology ‘is a way of showing the properties of a subject area and how they are related, by defining a set of concepts and categories that represent the subject’ (Ontology on Wikipedia)
Ontology is a difficult word, and in an effort to make the concept more comprehensible to new users Solid – Social Linked Data have started using the word vocabulary.
For a list of ‘ontologies that are fully documented, dereferenceable, used by independent data providers and possibly supported by existing tools.’ See Good Ontologies on the W3 wiki
See also plant ontologies, Emotion ontology for context awareness (EmOCA).
‘Knowledge taxonomies (usually mistermed “ontologies” these days) have become very popular recently, so there are lots of enthusiasts who don’t seem to realize that the subject has a very long and deep history. The original Roget’s thesaurus, the Dewey Decimal system, etc. As is by now extremely well known in Library Science, no single hierarchical organization can be ideal, although they can be workable – as is the modern version of Dewey and of the Library of Congress classification system. But to make them work requires a rather high degree of training and experience, more than can really be appreciated without studying those systems in some detail (i.e. I have and was amazed).’ From the c2wiki
References
See Cloud Time by Rob Coley and Dean Lockwood for a comment about the ontology of cloud culture.
WebVOWL: Web-based Visualization of Ontologies
Friend of a friend ontology on Wikipedia
OWL the Web Ontology Language features
Web Ontology Language on W3.org
Web Ontology Language on Wikipedia
QUTD – semantic specifications for units of measure, quantity kind, dimensions and data types