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 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 ) . 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  . 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
The following vocabularies and ontologies are currently described on semanticweb.org, 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!
|Dublin Core||RDF||1,364,337||28 October 2006|
|FOAF||OWL DL||1,194,871||27 July 2005|
|MetaVocab||RDF||441,790||16 February 2002|
|Basic Geo Vocabulary||RDF Schema||248,130||1 February 2006|
|BIO||RDF||220,228||5 March 2004|
|RSS 1.0||RDF Schema||201,786||6 December 2000|
|VCard RDF||RDF||181,962||22 February 2001|
|Creative Commons metadata||RDF Schema||112,216|
|WOT||OWL DL||97,292||23 February 2004|
|SIOC||OWL DL||42,911||11 April 2008|
|GoodRelations||OWL DL||5,000||1 October 2011|
|DOAP||RDF Schema||1,442||5 November 2005|
|Programmes Ontology||OWL 2||943||7 September 2009|
|Music Ontology||OWL 2||646||14 February 2010|
|OpenGUID||RDF Schema||1||24 September 2008|
|Provenance Vocabulary||OWL DL||1||25 August 2009|
|Pedagogical diagnosis||OWL DL||1||1 April 2012|
|DILIGENT Argumentation Ontology||OWL 2||1||13 September 2006|
- The Multi-Source Ontology (MSO) of the WebKB-2 knowledge server, an integration and extension of several general ontologies
- Open Biomedical Ontologies
- Ontology Design Patterns
- Semantic Web for Earth and Environmental Terminology (NASA)
- LKIF Core Ontology of Basic Legal Concepts
- OpenGALEN Medical Ontology
- Stanford Library of Ontologies
- An Ontology for Engineering Mathematics(paper)
- DOLCE Homepage
- DOLCE+Descriptions and Situations OWL ontologies
- Quantum Mechanics Ontology
- Engineering Mathematics Ontologies
- DAML List of Ontologies(outdated)
- SchemaWeb (List of Ontologies)
- Ontology for Long Term Ecological and Socioecological research
- Ontology Online
- Finance ontology Ontology on securities handling.
- OntoCAPE: A large-scale ontology for chemical process engineering