Subset dog animal
For more information, see InheritanceLink#Extensional_vs_Intensional.
SubsetLink ConceptNode: dogs ConceptNode: animals
means the same thing as:
EvaluationLink PredicateNode: Subset ListLink ConceptNode: dogs ConceptNode: animals
The SimilarityLink can be used to refine a simple subset relationship into a more complex "what kind of subset of" relationship.
In PLN the truth value of a SubsetLink relationship actually corresponds to a conditional probability over truth values, formally:
SubsetLink <TV> A B
where (Member X Y).s measures the degree to which x is a member of concept y, which can also be represented in the AtomSpace via a MemberLink.