I am surprised no one has mentioned schema.org. It is a much simpler standard and more widely used than RDF/OWL. Another point I think is that it is not in any

I am surprised no one has mentioned schema.org. It is a much simpler standard and more widely used than RDF/OWL. Another point I think is that it is not in any publishers interest to publish structured data, as it easily copy-able. For example, neither Amazon nor Wikipedia publishes using schema.org. It would make their data susceptible to 3rd party aggregators.