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• • Declarations for the built-in entities, e.g. owl:Thing, owl:Nothing, are excluded from the OWL refsets because they are implicitly presented in every OWL 2 ontology.
  • Class and property declarations are excluded from the OWL axiom refset to avoid duplication to the content that is represented by the RF2 concept file. Note, Class declaration and property declarations 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 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.

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Referenced component for an Axiom

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 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 . 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 D should be the referencedComponentId for this axiom.
• 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 conceptsprecoordinated 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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• SubClassOf represents the 

  Concept
  ShowParts term t 116680003 |Is a (attribute)|

   relationship between concepts in SNOMED CT. 

• SubObjectProperty SubObjectPropertyOf or SubDataProperty SubDataPropertyOf represents the 

  Concept
  ShowParts term t 116680003 |Is a (attribute)|

   relationship between attributes in SNOMED CT for Concept concept model object attributes and Concept concept model data attributes respectively.

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• Concept
  t 410662002 |Concept model attribute|

   should be represented as a class in the OWL axiom refset and SNOMED Ontology.

• Concept
  t 762705008 |Concept model object attribute|

    and its subconcepts should be represented as an object property in the OWL axiom refset and SNOMED Ontology. The 

  Concept
  ShowParts term t 116680003 |Is a|

   relationships among them should be represented as SubObjectProperty();

• Concept
  t 762706009 |Concept model data attribute|

   and its subconcepts should be represented as a data property in the OWL axiom refset and SNOMED Ontology. The relationship among them should be represented as SubDataProperty();

The metamodeling capacities of OWL 2 allow the punning for Classes and Properties. Both attribute concepts, 

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

 and 

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

, can be treated as Classes and Properties at the same time to enable the single root node of SNOMED CT. The following two SubClass axioms have been added in addition to SubProperty axioms in the OWL expression refset. These SubClass axioms represent and infer the 

Concept
t 116680003 |Is a|

relationships to 

Concept
t 410662002 |Concept model attribute (attribute)|

 that is a Class.

• SubClassOf(:762706009 :410662002)
• SubClassOf(:762705008 :410662002)

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 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

Attributes

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

• The attribute 

  Concept
  t 410662002 |Concept model attribute|

   should be represented as a Class in the OWL axiom refset. 

...

SourceId

...

TypeId

...

• The attribute

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

...

•  and 

...

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

...

•  should be represented as Classes and Properties as noted above.
• All descendants of 

• Concept
  t

...

• 762705008 |Concept model object attribute (attribute)|

Attribute

...

• should be represented as ObjectProperties.
• All descendants of 

  Concept
  t

...

• 762706009 |Concept model data attribute (attribute)|

...

•  should be represented as

...

Concept
t 410662002 |Concept model attribute|

...

• DataProperties.
• All the rest attributes in SNOMED CT should be represented as Classes

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• . 

Role Group

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.

An example for diagram representation of an OWL axiom
Image Modified

Modules and Axioms

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

During the transitional period, there should be only one active axiom in the OWL axiom reference set for each concept. This axiom will represent the set of all active relationships attributes (from the existing stated relationship file) for which the given concept is the source concept. This axiom overriding approach should only be used for the transition once. After the transition period, these axioms will be reviewed, and where appropriate will be split into multiple axioms as described in the Axiom addition approach.

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