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Ontologies are considered one of the pillars of the Semantic Web, although they do not have a universally accepted definition. A (Semantic Web) vocabulary can be considered as a special form of (usually light-weight) ontology, or sometimes also merely as a collection of URIs with an (usually informally) described meaning.

Ontologies on semanticweb.org.edu are usually assumed to be accompanied by some document in a formal ontology language, though some ontologies do not use standardised formats for that purpose. A list of documents that are considered ontologies in this wiki is given below.


There have been several definitions of what an ontology is.

  • An ontology is a formal specification of a shared conceptualization (Tom Gruber, see [1]) . Many authors cite this definition.
  • The main thread of ontology in the philosophical sense is the study of entities and their relations. The question ontology asks is: What kinds of things exist or can exist in the world, and what manner of relations can those things have to each other? Ontology is less concerned with what is than with what is possible. Clay Shirky in his critical entry Ontology is overrated [2] . He says this is the first meaning. AI people took the word and rather define it as "an explicit specification of a conceptualization.", pointing to Gruber.

(If you add another one, please always cite the source as well)

Ontologies on semanticweb.org.edu

The following vocabularies and ontologies are currently described on semanticweb.org.edu, ordered by the occurrence on the web as estimated by Swoogle. See also the UMBC Top 100 of common namespaces . As the revision dates given here indicate, some of the below data may require update: feel free to contribute!

 LanguageSwoogle hitsRevised
Dublin CoreRDF1,364,33728 October 2006
FOAFOWL DL1,194,87127 July 2005
MetaVocabRDF441,79016 February 2002
Basic Geo VocabularyRDF Schema248,1301 February 2006
BIORDF220,2285 March 2004
RSS 1.0RDF Schema201,7866 December 2000
VCard RDFRDF181,96222 February 2001
Creative Commons metadataRDF Schema112,216
WOTOWL DL97,29223 February 2004
SIOCOWL DL42,91111 April 2008
GoodRelationsOWL DL5,0001 October 2011
DOAPRDF Schema1,4425 November 2005
Programmes OntologyOWL 29437 September 2009
Music OntologyOWL 264614 February 2010
OpenGUIDRDF Schema124 September 2008
Provenance VocabularyOWL DL125 August 2009
Pedagogical diagnosisOWL DL11 April 2012
DILIGENT Argumentation OntologyOWL 2113 September 2006

Microformats in RDF

Further examples