<https://forum.mrw.it/threads/php-inserimento-dati-su-tabelle-collegate-1-m.46874/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://forum.mrw.it/threads/php-inserimento-dati-su-tabelle-collegate-1-m.46874/#post-183345>