Introduction

A discussion paper from the Content Managers Advisory Group, entitled Discussion Paper - Allowance of Extensions to Modify Core Content was submitted to SNOMED International management to resolve issues surrounding the interpretation of the allowable changes national extensions may make to 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.  This response proposes a set of policy statements that explicitly state what can and cannot be done to content of the International release by national extensions.

While this response is principality focused on the needs of national extensions, the general policies discussed here will apply to all extensions, regardless if they are directly dependent on the International release or another edition.  

Background

The primary concern expressed is the interpretation of Clause 4.1 of the SNOMED CT® AFFILIATE LICENSE AGREEMENT, which states: 

“Subject to clause 2.1.4, the Licensee may not modify any part of the SNOMED CT Core distributed as part of the International Release or as part of a Member’s National Release.”

Clause 2.1.4 states:

 “(The Licensor grants the Licensee, license to) modify the manner of formatting of the copy of the SNOMED CT Core distributed to the Licensee as part of the International Release or as part of a Member’s National Release”

 According to the discussion paper, there are two primary issues associated with this clause:

 "This restriction on modifications has been interpreted generally in two ways. 

1. The RF2 distribution must not be modified, beyond appending additional rows. Overwriting data in the distribution files - such that an extension violates the append only model is not allowed (editor's addition). Additionally, the full history provided by the international release must provided, i.e. extensions may not omit anything;

2. International components must not be modified.
   Overriding the international content through either:

• the addition of new versions for international components within extensions; or

• the addition of relationships to international concepts and changing their DL definition.

Restrictions covered by B have been shown to be impractical and prohibit proper quality terminology authoring."

Proposed actions allowed for National Extensions

The discussion paper proposes seven actions that national extensions may want to perform in the course of their content development and maintenance:

1. Create new concepts.

2. Fully define concepts they create.

3. Classify terminology extensions.

4. State additional IS A relationships against core (international) concepts.

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

6. Add additional defining (non-IS A) relationships to primitive international concepts.

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

The paper then goes into substantial detail justifying the need to perform each of these actions.  A request was forwarded to SNOMED International management for review and clarification of the interpretation of clause 4.1 and acceptance of the allowable proposed actions available to national extension managers.

This document attempts to clarify the feasibility of each of the proposed actions and provides justification for the acceptance or rejection of each, in order to make the interpretation of Clause 4.1 more clear.

Evaluation of proposed allowable actions for national extensions

The initial draft of this policy document was extensively discussed at the Editorial Advisory Group face-to-face meeting in London, 2017. The consensus at the conclusion of this discussion topic was:

• The interpretation by the EAG of section 2.1.4 was that of option A, i.e. "The RF2 distribution [of the International release] must not be modified... Overwriting data in the distribution files - such that an extension violates the append only model is not allowed...the full history [of] ...the international release must provided.
• Conversely, the full content of the original RF2 International release distribution must be extractable from any RF2 distribution of a national edition (combination of International and national content), without the need for any data transformation.
• The use cases for modifications to core international content were recognized as generally valid and recognized as potentially causing classification changes to inferred views of international content in a national release.
  
• All modifications to the International release must be appended to the RF2 files within a Module ID owned by the extension.  Addition of changes in the SNOMED International Module are not allowed.
• Substantive errors in or improvement to content in the International release that are mitigated by content in an extension should be forwarded to SNOMED International in a timely fashion to improve the quality of the International release.
  
  

In light of these conclusions, there are very few changes that an extension may NOT make to the International release provided the following are adhered to:

• These allowances are ONLY applicable to RF2 releases, where a full history of content changes is distributed
• RF1 distributions that are derived from RF2 extensions that involve changes to inferences in the International release are in violation of Clause 4.1 of the affiliate license (source of the changes cannot be tracked, original International release cannot be extracted)
• Classification inferences in an edition that result in differences from the International release must not be represented as SNOMED International content.
• Due to the changes to International classifications caused by modifications by national extensions, a disclaimer notifying users of the differences between the extension release and the International release must accompany the national extension distribution files.