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The ability to classify extensions is an essential part of leveraging the description logics represented in the International Release for the proper maintenance of extension content.  However, in some cases the results of classification may change the inferred relationships of existing core content.  

Proposed policy

1. In cases where the classification results in an inferred IS A relationship from the core to become transitive(i.e. redundant). This relationship from the core must be reactivated prior to the release.  I.e. transitive relationships may exist in a national edition as long as they originate from a different module from the extension.
   

State additional IS A relationships against core (international) concepts

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1. Addition of new stated IS A relationships to core content is not allowed.
2. Where a needed IS A relationship has been identified, a request to SNOMED International for addition of this relationship should be submitted as soon as possible.  These will be handled as high priority by the editorial staff. 

Retire (redundant) IS A relationships (not necessarily stated)

Redundant IS A relationship exist in SNOMED CT where variations in modeling style have been used and hierarchically related terms have been assigned as stated relationships. These are considered internal quality errors in the and are being incrementally addressed through the SNOMED CT Internal quality improvement program.  Many of these are already identified (See: https://dailybuild.ihtsdotools.org/qa/  Pattern 1) and are being addressed by SNOMED editors as resources allow.  Redundant relationships that impact extension structure should be reported to SNOMED International for prioritized disposition.  

Proposed policy

1. Inactivation of International release stated IS A relationships is not allowed. 
2. Relationships identified as redundant and impacting extension content should be reported to SNOMED Int'l as soon as possible to increase its priority.   
3. International stated relationships must not be retired. 
4. International inferred concept may be retired in a national edition is if it is redundant, but it must still be part of the transitive closure. 
5. Where retirement of stated relationships are needed, a request should be made to SNOMED International to promote correct the intermediate concepterror.
   

Add additional defining (non-IS A) relationships to primitive core concepts

The incomplete modeling of core content resulting in a plethora of primitive content is well-recognized.  However, correction of these deficiencies within a national extension can lead to a number of unintended consequences including: 1) the impact on the classification process and the potential change in meaning of descendent descendant concepts (i.e. loss of subtypes) 2) eventual remodeling of the primitive concept in the International release could lead to conflicts between the national edition and the International release.

It is recognized that there may be cases where proper structuring of a national extension requires the full definition of currently primitive core conte

, and (b) perhaps we should require NRCs who add defining attribute relationships to international concepts to submit these for promotion to / inclusion in the international edition. 

Of course, content and that the immediate needs of an extension do not coincide with the timing of International releases. The potential dangers of content divergence in national extensions by allowing definition of core primitive content must be recognized by extension managers prior to undertaking such an effort. It must also be recognized that allowing the definition of international concepts to be changed in an extension makes cross-border, cross-organisation exchange/management/querying of health records an even harder problem more difficult than it already is... so the more than can be done and shared in the international edition the better.

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Proposed policy

1. When needed to support national extension requirements, the addition of defining relationships to existing primitive core content is allowed, providing:
   1. the additions are consistent with the current International Machine readable concept model
   2. the additions are submitted to SNOMED International as soon as possible for inclusion in the International release

Retire content considered "inappropriate" - concepts, descriptions or relationships

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1. 1. Inactivation of components (concepts, descriptions, stated relationships) originating in the International release, by a national extension, is not allowed.
   2. Identified inappropriate components shall be communicated to SNOMED International via the content request system as internal quality errors to be addressed by the SNOMED International editorial team
   3. Components in the International release identified as inappropriate for a national extension may be excluded from the national release through refsets.  Components in the International release must not be inactivated simply because they are deemed inappropriate for national use. 
   4. The identification of issues in the international edition that impact a national extension must be added to a Content Request to escalate its priority for resolution by the SNOMED International editorial team  The identification of these errors as impacting a national extension will be added to the request in order to escalate its priority in resolution by the editorial team.