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1. The addition of the concept does not inactivate existing inferred IS A relationships except to insert a new proximal ancestor (the intermediate concept); i.e. does not change the International release transitive closure table (except to add the additional row representing the new intermediate ancestor relationship) change the transitive closure for the International Release, except to add additional rows that include the new intermediate concept). The transitive closure of the national edition must be a superset of the transitive closure of the international edition. This necessitates the retention of all transitive IS A relationships from the core.
2. No non-IS A inferred relationships stated defining attribute of core content are inactivated in the extension.
3. Inferred |is a| relationships should only be inactivated due to redundancy, but should still represent a valid relationship in the transitive closure. See "Retire (redundant) IS A relationships (not necessarily inferred)". 
4. Additional inferred defining relationships to not create crossovers (i.e. subtypes with attribute values that are supertypes of the values represented by the same attribute of the parent)
5. Additional inferred IS A relationships of subtypes do not represent a change in meaning as represented by the Fully Specified Name. 
6. The intermediate concepts are submitted for promotion to the international release as soon as possible.

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State additional IS A relationships against core (international) concepts

Missing stated IS A relationships for core content is usually the result of the existence of intermediate primitive concepts that editors are unaware of.  These intermediate primitive concepts are under review, but the volume makes it unlikely that all will be identified and resolved in the very near future.  Identification of these missing stated relationships by national extensions provides an opportunity for incremental improvement of the core terminology.   

Proposed policy

1. Addition of new stated IS A relationships to core content is not allowed.

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. Relationships identified as redundant should be reported to SNOMED Int'l as soon as possible to increase its priority.   
2. International stated relationships must not be retired. 
3. 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. 
4. Where retirement of stated relationships are needed, a request should be made to SNOMED International to promote the intermediate concept.
   

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 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, 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 than it already is ... so the more than can be done and shared in the international edition the better.

Proposed policy

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

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