code: def set_urn(self,urn):
          
          Type = self.session.get_class(surf.ns.ECRM['E55_Type'])
          Identifier = self.session.get_class(surf.ns.ECRM['E42_Identifier'])
          id_uri = "%s/cts_urn"%str(self.subject)
          try:
              id = Identifier(id_uri)
              id.rdfs_label = Literal(urn)
              id.ecrm_P2_has_type = Type(BASE_URI_TYPES % "CTS_URN")
              id.save()
              return True
          except Exception, e:
              raise e
docs: Change the CTS URN of the author or adds a new one (if no URN is assigned).