The SubsetLink denotes extensional inheritance between two Atoms. An example of a SubsetLink would be:

Subset dog animal


SubsetLink is also equivalent to an EvaluationLink whose PredicateNode is "Subset". Thus, for example:

SubsetLink
ConceptNode: dogs
ConceptNode: animals


means the same thing as:

EvaluationLink
PredicateNode: Subset
ConceptNode: dogs
ConceptNode: animals


## Naming subsets

The SimilarityLink can be used to refine a simple subset relationship into a more complex "what kind of subset of" relationship.

## PLN Semantics

In PLN the truth value of a SubsetLink relationship actually corresponds to a conditional probability over truth values, formally:

SubsetLink <TV>
A
B


with

${\displaystyle TV.s={\frac {\sum _{x}f_{\wedge }(({\text{Member}}\ x\ B).s,({\text{Member}}\ x\ A).s)\times x.s}{\sum _{x}({\text{Member}}\ x\ A).s\times x.s}}}$

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.