Relation pm#file_element (?,document_element)
  supertype:  file_or_file_element (?,description_container)
     supertype:  Description (?,entity)  to specify an account of the content of a resource; in WebKB, pm#topic or pmdescr SHOULD BE USED INSTEAD
        supertype:  binary_relation (?,?)  in WebKB, most relation types are binary and some have a variable number of arguments (as in KIF), hence this type is currently only specialized by types that I do not want to see as direct subtypes of pm#relation
           supertype:  relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
              >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type