Relation p3p#purposeOptIn (Statement,PurposeClass)  Data may be used for this purpose only when the user affirmatively requests this use.
  supertype:  purpose (Statement,PurposeClass)  Defines the purpose for which the data practise is employed
     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