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The OWL Axiom Reference Set is designed to cover all logic definitions in SNOMED CT. A concept can be defined by one or more axioms in the same module or different modules. Each axiom is represented by a string in

Gloss
t OWL Functional Syntax GlosTerm OWL Functional Syntax

 in the owlExpression field. Each concept is represented by a concept ID in the referencedComponentId in the refset. The referencedComponentId has no impact on the semantics of the axioms and it is not used for any logical reasoning. The following rules should be followed when assigning the referencedComponentId for an axiom:

• If an axiom is in the form of SubClassOf(C D) or EquivalentClasses(C D) where concept C is a precoordinated concept, the concept ID of C should be the referencedComponentId for this axiom.
• If an axiom is in the form of SubPropertyOf(r s) or EquivalentProperties(r s) where attribute r is a precoordinated concept, the concept ID of r should be the referencedComponentId for this axiom.
• If an axiom is in the form of SubClassOf(C D) where concept C is NOT a precoordinated concept and D is a precoordinated concept. This is a General Concept Inclusion (GCI) axiom. Because concept C is a sufficient but not necessary condition for concept D, the concept ID of concept D should be the referencedComponentId for this axiom. Note, if C is a precoordinated concept, this SubclassOf axiom is NOT a GCI axiom and the concept D should not be assigned as the referencedComponentId.
• If an axiom is in the form of SubObjectPropertyOf(u t) where attribute u is NOT a precoordinated concept and attribute t is a precoordinated concept. The concept ID of t should be the referencedComponentId for this axiom. e.g. SubObjectPropertyOf(ObjectPropertyChain(:r :s) :t)
• If an axiom is in the form of SubClassOf(C D) or EquivalentClasses(C D) where both C and D are NOT precoordinated concepts, this is a GCI axiom and the referencedComponentId should be 733929006 |General concept inclusion axiom (metadata)|.
• If an axiom is in the form of DisjointClasses(C D) where both C and D are precoordinated concepts, the concept ID of C should be the referencedComponentId for this axiom. Then the axiom DisjointClasses(D C) is redundant.
• The disjointness in more than two Classes can be represented as DisjointClasses(C D E …) where all classes are precoordinated concepts. The concept 

  Concept
  t 787776007 |Disjoint classes axiom (OWL metadata concept)|

   should be the referencedComponentId for this axiom.

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For inferred relationships in the Necessary Normal Form (NNF), SubClassOf, SubObjectProperty and SubDataProperty in the OWL axiom refset should be represented as

Concept
ShowParts term t 116680003 |Is a|

 relationships. The explanation for the Necessary Normal Form and the rules for calculating the NNF can be found in section 2.5. Generating Necessary Normal Form Relationships from the OWL Refsets. the NNF can be found in section 2.5. Generating Necessary Normal Form Relationships from the OWL Refsets. 

Representation of concrete domains

DataHasValue class expression should be used for a 

Concept
t 762706009 |Concept model data attribute (attribute)|

 with a particular literal value that is specified in the SNOMED OWL Logic profile specification. The DataSomeValuesFrom and DataAllValuesFrom class expressions should not be used. For example, the value of

Concept
t 1142135004 |Has presentation strength numerator value (attribute)|

 should be represented as:

    DataHasValue(:1142135004 "50"^^xsd:decimal)

Unfortunately, the xsd:boolean data type is out of the scope for the OWL 2 EL profile (https://www.w3.org/TR/owl2-profiles/#Entities). In order to have a consistent representation and clear semantics, the boolean values should be represented by the concept 

Concept
t 31874001 |True (qualifier value)|

 and 

Concept
t 64100000 |False (qualifier value)|

. The attribute should be a subtype of 

Concept
t 762705008 |Concept model object attribute (attribute)|

 with a constraint in the SNOMED CT Machine Readable Concept Model that only these two values are in the range and the attribute cardinality is 0..1.

Note, trailing zeros are optional for the decimal data type in SNOMED CT. If the fractional part is zero, the period and following zero(es) can be omitted. For example, 2 is equivalent to 2.0. In particular, trailing zeros are prohibited for medicinal products in SNOMED CT because of clinical safety concerns. This 'trailing zero' policy should be applied in the same subject area of SNOMED CT for consistent classifications because the ELK reasoner has an incomplete implementation of concrete domains. However, it is possible that other subject areas, e.g. clinical findings, could allow for trailing zeros if it is desirable.

Attributes

SNOMED CT is based on concepts, with attributes also being represented as concepts. However, attributes need to be represented as properties in the OWL axiom refset. The following rules should be followed.

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Role groups must be explicitly stated and represented by the concept 

Concept
t 609096000|Role group (attribute)|

 as an object property in the OWL axiom refset. In the diagram of stated relationships in the OWL axiom refset, the attribute 

Concept
t 609096000|Role group (attribute)|

 should still be represented by a circle rather than an object property. The role group should not be omitted for self-group attributes where there is only a single attribute in a role group.

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This approach is different to the Axiom addition. The extension takes over the ownership of an axiom from the International Edition and overrides the axiom. 

Whichever the approach is taken by extensions, either Axiom addition or Axiom overriding, it must follow the General Authoring Principles for extensions. Any modifications resulting in changes to the classification of international content must be accompanied by a disclaimer notifying users of the differences between the extension edition and the International Edition. These changes should be forwarded to SNOMED International in a timely fashion to improve the quality of the International Edition for all users. Please note that modifications of this kind pose a risk to the comparability and interoperability of data captured using different SNOMED CT editions.

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The versioning is at the axiom level for a concept in the OWL axiom refset. This means that there is only one effectiveTime for each version of an axiom, which may have multiple relationships. The changes to any relationships in the current editing tool will trigger an "update" of the most recent version of the relevant axiom. Versioning The versioning at the axiom level (, where each axiom may represent multiple relationships) , is different to from the versioning of each individual relationship in the relationship file.

Any changes to the NNF should have a corresponding history of changes in the OWL axiom refset. This will ensure that all entries in the NNF can be derived from the OWL refset except for those relationships listed in the table 2.4-1. The NNF will still have the computed effectiveTime for each inferred relationship. The version of each inferred relationship can be derived from the OWL refset, but it is not true in reverse.

It is permitted to make modifications to a published axiom without inactivation by the owner of the module, by creating a new version of the axiom with the same UUID and a new effectiveTime. Since any modification to an axiom could potentially alter its meaning, it is not necessary to inactivate an axiom and create a new axiom. It is also not necessary to reinstate an inactivated axiom in the previous release when the same axiom is created as a new expression. This approach can simplify the tooling and authoring process and it is a different approach to the history of changes to the individual relationship.

However, an axiom must be inactivated in the following situations:

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Special notes on axioms during the transitional period from the stated relationship file to the OWL axiom refset

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