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  • Laboratory for Applied Ontology (LOA)
  • Open, International, Virtual Community of Practice on Ontology, Ontological Engineering and Semantic Technology (ONTOLOG)
  • Web-Ontology Working Group (WebOnt)

  • Watson (Watson)
  • OntoSelect (OntoSelect)
  • The Generalized Upper Model 2.0
  • EuroWordNet
  • MIKROKOSMOS (not freely available any more)
  • OntoBroker (Inference Engine)
  • Protégé (Ontology Editor)
  • UMLS MetaThesaurus
  • CyC Knowledge Server (Knowledge Base / Inference Engine)
  • WordNet - a Lexical Database for English
  • Suggested Upper Merged Ontology (SUMO)
  • MindNet
  • ICD: International Code of Diseases
  • UMLS Semantic Network
  • CycSecure
  • OntoMat (Ontology-based Annotation Tool)
  • Medical Subject Headings
  • Sigma Knowledge Engineering Environment
  • SNOMED: Systematized Nomenclature of Medicine
  • OntoEdit (Ontology Editor)
  • OWL Ontology Library
  • GermaNet

From a theoretical point of view, ontology is the metaphysical study of the nature of being and existence. In practice, an ontology is normally viewed as a formal representation of all semantic objects and their connections in a Universe of Discourse. Mapping these semantic objects onto language units (words, phrases, text segments, etc.) is the task of semantic processing in NLP.