Function owl#cardinality (restriction -> nonnegative_integer)  for onProperty(?restrClass,?rel) and cardinality(?restrClass,n), read: i instance of ?restrClass if and only if there are exactly n distinct j with ?rel(i,j)
  supertype:  relation_from_restriction (restriction,*)
     supertype:  relation_from_class (class,*)
        supertype:  relation_from_type (type,*)  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property
           supertype:  relation_from_collection (collection,*)
              supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
                 >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
              supertype:  what_relation (*)
                 supertype:  wh-/how_relation (*)  this type permits to categorize relations according to the usual who/what/why/where/when/how questions ; this is a traditional but very subjective and ineffective 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