The Axioms are statements or propositions which are regarded as being established, accepted, or self-evidently true in the domain. The OWL axioms are in the scope for the OWL axiom refset if they are allowed in the SNOMED CT Logic Profile Specification. The following Annotation axioms are in the scope of Logic Profile, however they are excluded from and Class declarations are generally excluded from the OWL axiom refset to avoid duplication to the RF2 files:

• Annotation Axiom Annotation Assertion – - Descriptions can be represented as annotation assertions. However, they They are excluded from the OWL refset to avoid duplication to the RF2 description file.

The transformation from the OWL refset to OWL ontology document should process description file and language refset when descriptions are included. They should be represented by the following annotation properties for a given language refset.

• • rdfs:label - if present, it is RF2 fully specified name
  • skos:prefLabel - if present, it is RF2 preferred term
  • skos:altLabel - if present, it is RF2 acceptable synonym
  • skos:definition - if present, it is RF2 definition
    
    
• Declaration

• • Declarations

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• • Declarations for the built-in entities, e.g. owl:Thing, owl:Nothing, are excluded from the OWL Refset because they are implicitly presented in every OWL 2 ontology.
  • Class declarations are excluded from the OWL Refset because the Concept file represents the same information. 138875005 |SNOMED CT Concept (SNOMED RT+CTV3)| is the only concept needs to be declared in the OWL axiom refset.

Declarations are included in the OWL refset.

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• • refset to avoid duplication to the content that are represented by the RF2 concept file. Note, Class declaration should be included in cases where an entity type cannot be derived from the existing axiom.

However, property declarations should be included in the OWL

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refset to reduce the implementation burden for deriving such information at runtime. The property declarations include all attributes for SNOMED CT concept modeling. These attribute concepts must be excluded from the Class declarations.

Concept Defined by Axiom

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

Gloss
t OWL Functional

-Style Syntax in

Syntax GlosTerm OWL Functional Syntax

 in the owlExpression field.
Concepts are Each concept is represented by a concept IDs ID in the referencedComponentId in the refset. The association between axiom and concept should follow the following rules:

• If an axiom is in the form of SubclassOfSubClassOf(C D) or EquivalentClasses(C D) where concept C is a precoordinated concept, this axiom is a definition of concept C and concept id the concept ID of C should be the referencedComponetId for this axiom.
• If an axiom is in the form of SubclassOfSubClassOf(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 ID of D should be the referencedComponentId for this axiom.
• If an axiom is in the form of SubclassOfSubClassOf(C D) or EquivalentClasses(C D) where both C and D are NOT precoordinated concepts, this is a GCI axiom and the referencedComponetId 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 referencedComponetId for this axiom.

The definition status of a concept is 

Concept
ShowParts term t 900000000000073002|Sufficiently defined concept definition status (core metadata concept)|

 if the concept has one EquivalentClasses axiom no matter other associated axioms are SubClassOf or EquivalentClasses.

Representation of |is a| Relationships

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For inferred relationships in the Necessary Normal Form (NNF), SubclassOf, SubObjectProperty and SubDataProperty in the OWL 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 following additional two 

Concept
ShowParts term t 116680003 |Is a|

 relationships should always be included in the inferred relationship file because they cannot be derived from the OWL axiom refset.

Attribute

SNOMED CT is based on concept and attribute is also concept. However, a property cannot be a subproperty of a class in OWL because class and property are disjoint.
Descendants of 

Concept
t 410662002|Concept model attribute (attribute)|

should be represented as either ObjectProperties or DataProperties in the OWL axiom refset. The rest SNOMED CT attributes including 

Concept
t 410662002|Concept model attribute (attribute)|

 should be represented as Classes in the OWL axiom refset.

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

There should be only one active axiom in the reference set for all active relationships in conjunction for a concept at that snapshot across modules during the period of transformation from the existing stated relationships file to the OWL axiom reference set. Therefore, this is the axiom overriding approach and should only be used for the transformation once. Then, these axioms should be reviewed and many of them could be more suitable for multiple axioms.   

If a dependant module (e.g. an extension) adds relationships to that concept, this will result in a new version of the axiom is added to the OWL reference set with the addition. This new version must be created if any of the relationships from the viewpoint of the module's dependencies changes, regardless of whether that change is on the module in question or not. For example,

Results in two versions of a single OWL reference set entry