A qualifying characteristic is expressed by an attribute-value pair. The attribute may have one value, from a range of values, based on the domain's concept model. If a particular qualifying characteristic is applied to a concept, the resulting expression represents a more tightly defined subtype of that concept.

Clinical expressions using SNOMED CT concepts can be of two types: precoordinated expressions, which use a single SNOMED CT concept identifier; and postcoordinated expressions, which contain more than one SNOMED CT concept identifier.

For example,