RANGE is short for ``range restriction.'' Specifying a RANGE restriction of a relation is a way to constrain the class of objects which participate as the last argument to the relation. For any tuple <d1 d2 ...dn r> in the relation, if class T is a RANGE restriction of the relation, r must be an instance of T.
RANGE restrictions are very helpful in maintaining ontologies. One can think of a range restriction as a type constraint on the value of a function or range of a relation. Representation systems can use these specifications to classify terms and check integrity constraints.
If the restriction on the range of the relation is not captured by a named class, one can use specify the constraint with a predicate that defines the class implicitly, coerced into a class. For example, (kappa (?x) (and (prime ?x) (< ?x 100)))
denotes the class of prime numbers under 100.
It is consistent to specify more than one RANGE restriction for a relation, as long as they all include the EXACT-RANGE of the relation.
Note that range restriction is true regardless of what the restricted relation is applied to. For class-specific range constraints, use slot-value-type.
(<=> (Range ?Relation ?Type) (And (Relation ?Relation) (Class ?Type) (Subclass-Of (Exact-Range ?Relation) ?Type)))