The Resource Description Framework (RDF), together with its
extension RDF Schema, is a logical formalism that allows
formalizing information models in the form of RDF vocabularies
and representing propositional information on the Web, embedded in web
pages or in the form of special web data sources. OWL extends RDF by
adding many additional language elements for expressing constraints,
equalities and derived classes and properties in the context of defining
vocabularies. Unfortunately, both RDF and OWL have many usability issues.