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ISWC 2014 paper by Robert Meusel, Petar Petrovski, and Christian Bizer
getSchema's RDFa Lite extractor is a REST web service to extract RDF  data from RDFa Lite  annotations and provide the semantic information as N-Triples  , N3  and JSON .
More information about RDFa
online Version der aktuellen Ausgabe des Handbook of Ontologies
This site is a complementary effort by people from the Linked Data community to support Schema.org deployment and usage with a special focus on Linked Data:
Use the Rich Snippets Testing Tool to check that Google can correctly parse your structured data markup and display it in search results.
Knowledge Representation Ontology
Top-Level Ontologie von John Sowa
WordNet a lexical database for the English language