Table of Contents

Introduction

A discussion paper from the Content Managers Advisory Group, entitled Discussion Paper - Allowance of Extensions to Modify Core Content has been submitted to SNOMED International management to resolve issues surrounding the interpretation of what national extensions are allowed to modify in the International release of SNOMED CT.  The discussion paper outlines a number of proposed clarifications to the interpretation of what is allowed and details the requirements for those changes.

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The creation of intermediate concepts necessarily results in changes to the relationships in the core terminology.  These changes can be of almost any type including: assignment of new parent(s), retirement of inferred or stated parents, inheritance of new/additional defining relationships, removal of inferred relationships by the classifier, etc. 

Proposed policy

SNOMED International recognizes that SNOMED CT is not always comprehensive in its terminological coverage in particular domains and that there exist "gaps" in the hierarchies, where concept coverage is not adequate for extensions.  It is proposed that intermediate concepts may be added to extensions under the following guidelines:

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)
2. No inferred relationships of core content are inactivated
3. Additional inferred defining relationships to not create crossovers
4. Additional inferred IS A relationships of subtypes do not represent a change in meaning. 

Fully define concepts they create

Full definition of intermediate concepts will in many cases result in the reassignment of core relationship due to inferences assigned from the classifier (see next section).

Proposed policy

Classify terminology extensions

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, 

Proposed policy

State additional IS A relationships against core (international) concepts

Proposed policy

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

Proposed policy

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

Proposed policy

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

Proposed policy