Unlike vanilla XML, RDF vocabularies can be freely mixed together in data without prior agreement. So you often see ad-hoc combinations of Dublin Core, RSS1, MusicBrainz, RDF-calendar, FOAF, Wordnet, thesaurus, Geo-info etc etc frequently deployed togethe
xmlns.com is an internet domain created for the purposes of simple Web namespace management. The rationale for registering xmlns.com was to secure a short, memorable domain suitable for naming concepts for use in RDF and XML vocabularies.