RDF/XML
RDF/XML is a syntax, defined by the W3C, to express an RDF graph as an XML document. RDF/XML is sometimes misidentified as simply RDF because it was introduced alongside the other W3C specifications defining RDF and was historically the first W3C official RDF serialization format.
RDF/XML is the primary exchange syntax for OWL 2, and must be supported by all OWL 2 tools.