Relation SUBCLASS-OF

Class C is a subclass of parent class P if and only if every instance of C is also an instance of P. A class may have multiple superclasses and subclasses. Subclass-of is transitive: if (subclass-of C1 C2) and (subclass-of C2 C3) then (subclass-of C1 C3).

Object-centered systems sometimes distinguish between a subclass-of relationship that is asserted and one that is inferred. For example, (subclass-of C1 C3) might be inferred from asserting (subclass-of C1 C2) and (subclass-of C2 C3). The functional interfaces to such systems might call the asserted form something like `parents' and the inferred form `ancestors'. However, both are logically identical to subclass-of; distinctions based on inference procedures and the current state of the knowledge base are not captured in this ontology.

Instance-Of: Relation, Transitive-relation

Arity: 2

Domain: Class

Range: Class

Axioms:

(<=> (Subclass-Of ?Child-Class ?Parent-Class)
     (And (Class ?Parent-Class)
          (Class ?Child-Class)
          (Forall (?Instance)
                  (=> (Instance-Of ?Instance ?Child-Class)
                      (Instance-Of ?Instance ?Parent-Class)))))

• Defined in theory: Frame-ontology
• Source code: frame-ontology.lisp

Notes:

• See-Also: direct-subclass-of
• See-Also: In CycL, subclass-of is called #%allGenls because it is a slot from a collection to all of its generalizations (superclasses).

  In the KL-ONE literature, subclass relationships are also called subsumption relationships and ISA is sometimes used for subclass-of.

• Why is it called Subclass-of instead of subclass or superclass?

  Because the latter are ambiguous about the order of their arguments. We are following the naming convention that a binary relationship is read as an english sentence `Domain-element Relation-name Range-value'. Thus, `person subclass-of animal' rather than `person superclass animal'.