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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)|.
However, 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 - a new axiom with inclusion of the axiom from the dependant module (e.g. international release) as part of the axiom. The new axiom has the same UUID from the dependant module 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 (e.g. 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.

No matter which approach is taken, the transitive closure of the inferred

Versioning for Axioms

The versioning is at the axiom level for a concept in the OWL refset. It means that there is only one effectiveTime for an axiom that might have multiple relationships. The changes to any relationships in the current editing tool will trigger an "update" of axiom with the latest effectiveTime. They are different to the versioning at individual relationship level in relationship files.
Any changes to the NNF should have a history of changes in the OWL refset. This will ensure that all entries in the NNF can be derived from the OWL refset except relationships between attributes and concepts explained in the section 2.4.2. The NNF will still have the computed effectiveTime for each inferred relationship. The version of each relationship can be derived from the OWL refset but it is not true in reverse.
It is allowed to make direct modification to a published axiom without inactivation. The same UUID should be used with a new effectiveTime. 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 new expression. This approach can simplify the tooling and authoring process and it is different approach to the history of changes to individual relationship.
However, an axiom must be inactivated in the following situations:

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