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If you're looking for ontologies: https://archivo.dbpedia.org/ https://lov.linkeddata.es/ But there's maybe 5k ontologies, how do you hope to overview them and learn about them? You should start from a specific (narrow) problem domain.


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Are these required and recommended properties only a thing which is understandable for the Google search algorithms to work well? Yes. Follow additional guidelines in the documentation for your specific type. E.g., for Movie: required properties are name and image. See also https://github.com/schemaorg/schemaorg/issues/1715.


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Your question shows <> which is not a valid property or wildcard. You cannot use property variables (wildcards) in property paths. So you need to understand the structure of how dct:subject and skos:broader are used, and exploit that. I happen to know that dct:subject links pages to categories skos:broader makes the category hierarchy I should warn ...


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