Relation pm#Higgins_object_property (?,?)
  subtype:  contextRelationship  contextId  attribute  complexMetadata
  supertype:  Higgins_property (?,?)
     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