Relation p3p#purpose (p3p#Statement,p3p#PurposeClass)  Defines the purpose for which the data practise is employed
  subtype:  p3p#purposeAlways  p3p#purposeOptIn  p3p#purposeOptOut
  supertype:  pm#P3P_relation (?,?)
     supertype:  pm#relation_coming_from_an_ontology (*)
        supertype:  pm#relation_for_an_application (*)  relation introduced by an application
           supertype:  pm#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:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type