Relation rdfs#sub_property_of (binary_relation_type,binary_relation_type)  in WebKB, use the link '<'
  equal:  sub_property_of
  supertype:  subrelation (relation_type,relation_type)  if the common reading conventions of parameters had been respected, this type would have been named subclass_of; every tuple of the 1st argument (r1) is also a tuple of the 2nd argument (r2), i.e. if r1 holds for some arguments arg_1, arg_2, ... arg_n, then the r2 holds for the same arguments; a consequence of this is that a relation and its subrelations must have the same valence
     supertype:  supertype (type,type)  in the FT notation, the '<' link is only used to connect to a "strict" supertype
        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
        supertype:  generalizing_type (?,type)  fuzzy category, DO NOT USE DIRECTLY
           supertype:  partial_ordering_relation (?,?)  this category only serves structuration purposes: it is instance of pm#partial_ordering_relation_type which is not instance of pm#class_of_inheritable_relation_type
              supertype:  reflexive_relation__reflexiverelation (?,?)  this category only serves structuration purposes: it is instance of pm#reflexive_relation_type which is not instance of pm#class_of_inheritable_relation_type
                 supertype:  binary_relation_with_particular_mathematical_property (?,?)
                    supertype:  relation_with_particular_mathematical_property (*)
                       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
              supertype:  antisymmetric_relation__antisymmetricrelation (?,?)  this category only serves structuration purposes: it is instance of pm#antisymmetric_relation_type which is not instance of pm#class_of_inheritable_relation_type
                 supertype:  binary_relation_with_particular_mathematical_property (?,?)
              supertype:  transitive_relation (?,?)  this category only serves structuration purposes: it is instance of pm#transitive_relation_type which is not instance of pm#class_of_inheritable_relation_type
                 supertype:  binary_relation_with_particular_mathematical_property (?,?)
  supertype:  relation_to_another_binary_relation_type (binary_relation_type,binary_relation_type)
     supertype:  relation_from_binary_relation_type (binary_relation_type,*)
        supertype:  relation_from_relation_type (relation_type,*)
           supertype:  relation_from_type (type,*)  type of relations from a concept/relation type, i.e. in RDFS terminology, from a class or a property