Unique identifier for the OWL Serialization in XML.

'http://www.w3.org/ns/formats/OWL_XML' is the URI. OWL XML is defined by the “OWL 2 Web Ontology Language, XML Serialization” W3C Recommendation. It has a media type: ‘application/owl+xml’ and a preferred suffix: ‘.owx’. (See further details on the Media Registration.)