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The editing of entries in the OWL refsets can only be performed by the owner of that module. In general, the extensions must not modify the OWL refset entries from the dependant modules, such as 900000000000445007|International Health Terminology Standards Development Organisation maintained module (core metadata concept)|.
SNOMED CT extensions can add new axioms for the concepts in the dependant module (e.g. international release ) by following the General Authoring Principles for extensions. A new axiom in the extension module can be represented by two approaches with different semantics.

• Axiom override Axiom overriding - a new axiom with inclusion of the axiom from the dependant module international release as part of the axiom. The new axiom has the same UUID from the dependant module international release with a new effectiveTime and module id in the extension. This approach should be avoided because it overrides the axiom from the dependant module.
• Multiple axioms - a new axiom without inclusion of the axiom from the dependant module international release as part of the axiom. The new axiom has a new UUID and effectiveTime in the extension. This approach provides multiple axioms for an concept in the extension module.

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Special notes on axioms during the period of transformation from stated relationship file 

Each concept can only have one axiom 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, 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.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,

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