SNOMED CT supports the following types of class restrictions:

• existential quantification to a class expression (ObjectSomeValuesFrom)

• intersection of classes (ObjectIntersectionOf)

• existential quantification to a literal (DataHasValue)

SNOMED CT supports the following axioms, all of which are restricted to the allowed set of class expressions:

• class inclusion (SubClassOf)

• class equivalence (EquivalentClasses)

• object property inclusion (SubObjectPropertyOf) with or without property chains, and data property inclusion (SubDataPropertyOf)

• class disjointness (DisjointClasses)

• property equivalence (EquivalentObjectProperties and EquivalentDataProperties),

• transitive object properties (TransitiveObjectProperty)

• reflexive object properties (ReflexiveObjectProperty)

The following constructs are not supported in SNOMED CT:

• assertions (SameIndividual, DifferentIndividuals, ClassAssertion, ObjectPropertyAssertion, DataPropertyAssertion, NegativeObjectPropertyAssertion, and NegativeDataPropertyAssertion)

• functional data properties (FunctionalDataProperty)

• keys (HasKey)

• domain restrictions (ObjectPropertyDomain and DataPropertyDomain)

• range restrictions (ObjectPropertyRange and DataPropertyRange)

• intersection of data ranges (DataIntersectionOf)

• existential quantification to a data range (DataSomeValuesFrom)

• existential quantification to an individual (ObjectHasValue)

• self-restriction (ObjectHasSelf)

• enumerations involving a single individual (ObjectOneOf) or a single literal (DataOneOf)

• universal quantification to a class expression (ObjectAllValuesFrom) or a data range (DataAllValuesFrom)

• cardinality restrictions (ObjectMaxCardinality, ObjectMinCardinality, ObjectExactCardinality, DataMaxCardinality, DataMinCardinality, and DataExactCardinality)

• disjunction (ObjectUnionOf, DisjointUnion, and DataUnionOf)

• class negation (ObjectComplementOf)

• enumerations involving more than one individual (ObjectOneOf and DataOneOf)4

• disjoint properties (DisjointObjectProperties and DisjointDataProperties)

• irreflexive object properties (IrreflexiveObjectProperty)

• inverse object properties (InverseObjectProperties)

• functional and inverse-functional object properties (FunctionalObjectProperty and InverseFunctionalObjectProperty)

• symmetric object properties (SymmetricObjectProperty)

• asymmetric object properties (AsymmetricObjectProperty)

Rationale for exclusions

There are a number of notable exclusions from the SNOMED CT Logic Profile, which are features often desired for definition of content. These have been excluded due to their additional complexity and/or impact on reasoning times with current hardware and algorithms, outweighing the benefit they provide.

Largely these notably excluded features are:

• universal quantification to a class expression (ObjectAllValuesFrom)

• disjunction (ObjectUnionOf, DisjointUnion, and DataUnionOf)

• class negation (ObjectComplementOf)

The primary motivation for excluding these features and remaining within the OWL 2 EL profile is to ensure classifiers can reason over SNOMED CT content and expressions in a reasonable timeframe. This computational time has implications not just for computing inferred forms for release publication, but also for calculating subsumption relationships for expressions in implementations, particularly affecting runtime expression subsumption.

Therefore while some of the features are desirable for content modelling, moving to OWL 2 DL incurs too high a cost to implementation of SNOMED CT to be supportable at this time. If these features become reasonably practical to add in future (e.g. due to advancements in reasoner technologies) then they may be added. Until that time, modelling patterns must be devised to address the content and use cases which would benefit from these features to work around their absence.

All OWL 2 DL features not included in OWL 2 EL are excluded from the SNOMED CT Logic Profile. Additionally the following features which are in the OWL 2 EL profile are not included in the SNOMED CT Logic Profile:

• domain and range constraints are not supported in the SNOMED CT Logic Profile as they are supported via the SNOMED CT Machine Readable Concept Model rather than in the Description Logic constructs

• as individuals are not supported in SNOMED CT due to a lack of overall utility in SNOMED CT’s context, individual related constructs are not supported

• support exists for DataHasValue; however, usage is restricted to prohibit ranges