A subset definition in which the membership is represented by a set of rules. These rules specify the necessary conditions that must be met for inclusion within the subset.
- An extensional definition of the members of subset of SNOMED CT concepts can be represented as a set of rules (e.g. concepts that are types of respiratory disease characterized by edema).
- The standard way to represent an intensional definition of a subset of SNOMED CT concepts is to use the SNOMED CT expression constraint language.
- The standard way to distribute an intensional definition of a subset of SNOMED CT concepts is as a row in a query specification reference set containing the expression constraint.