Relation p3p#user.department__department (StructuredDataElement,User.department)  department
  extends:  "user"
  supertype:  dataElementComponent__data_element_property (StructuredDataElement,?)  A part of a data structure
     supertype:  P3P_relation (?,?)
        supertype:  relation_coming_from_an_ontology (*)
           supertype:  relation_for_an_application (*)  relation introduced by an application
              supertype:  relation_playing_a_special_role (*)  this type permits to categorize relations according to their roles ; this is a traditional but quite subjective way of categorizing relations
                 >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type