The requirements for representing postcoordinated clinical meanings in health records, messages and expression associations are:

Requirement M1: Unambiguous meaning

An expression must be able to specify one unambiguous meaning, independently of the implementation environment.

Requirement M2: Conformance to concept model

Expressions must conform to the rules defined by the SNOMED CT concept model, or be transformable into an expression that conforms to the SNOMED CT concept model. For example, expressions with a clinical finding that is refined using the attribute 272741003 | Laterality| , can be transformed into a conformant expression by applying the laterality to every lateralizable body structure within the definition of the clinical finding. Please note that expressions may either conform to the international SNOMED CT concept model, or a local (e.g. national) extension to the concept model. For more information please refer to For more information please refer to section 12.3.17 and section 12.4.15 of the Terminology Services Guide.

Requirement M3: Subset of SNOMED CT's Description Logic profile

The logical features provided by SNOMED CT compositional grammar must be a subset of those supported by SNOMED CT's Description Logic profile. This profile is primarily based on OWL 2 EL, however some additional features (which are still able to be classified in polynomial time) may also be included. This ensures that all clinical meanings expressed using SNOMED CT compositional grammar can be translated into an equivalent representation in OWL and classified in polynomial time.

Requirement M4: Functional requirements

The logical model must support the following capabilities:



Concept reference

The ability to reference a precoordinated SNOMED CT concept using its identifier and optional human-readable term.

Intersection / Conjunction

The ability to connect two focus concepts via a logical AND operator.


The ability to refine (or specialise) the meaning of an expression using one or more attributes values.

Attribute group

The ability to group a collection of attributes which operate together as part of a refinement.


An attribute-value pair which further refines the meaning of the expression


The ability to include an expression as the value of an attribute

Concrete values

The ability to use integers, decimals, strings and booleans as attribute values

Definition status

The ability to specify whether the clinical meaning is 'equivalent to' or a 'subtype of' the expression.