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This section covers several general topics related to SNOMED CT release files. 
The next two sections provide the detailed specifications of the release files:

3. Component Release Files Specification

Files that represent the main SNOMED CT components:

  • Concepts

  • Descriptions

  • Relationships

4. Reference Set Release Files Specification

Files that customize and enhance SNOMED CT by representing:

  • Subsets of concepts and descriptions
  • Maps to other code systems
  • Language and dialect preferences for different terms
  • Annotation of components
  • Associations between components
  • Other forms of configuration and extensibility

Additional information is provided in the Terminology Services Guide, a separate document that includes guidance on Representing Terminology Data and Importing SNOMED CT Release Files.

Historical Note on Current and Previous Release File Formats

The standard format in which  SNOMED CT has been distributed since 2012 is known as  Release Format 2(RF2). It was developed in response to extensive feedback on the original release file format, now known as Release Format 1(RF1), in which SNOMED CT was distributed between its first release in 2002 and 2012. The SNOMED CT International Edition is no longer distributed in RF1. However, a conversion tool to general RF1 style files from the RF2 release files was made available during a transition period.

The key enhancements in RF2 were:

  • More robust and consistent version representation;
  • Inclusion of a moduleId and module dependency mechanism, which together enable modularization of releases while representing dependencies between modules;
  • Reference sets to provide an extensible and versionable way to configure  SNOMED CT. Including support for subsets, maps, annotations, alternative hierarchies, etc.;

  • Use of an added hierarchy to represent metadata about the structure of SNOMED CT itself.

In common with the earlier release format RF2 specifies files that: 

  • Represent the components of SNOMED CT: (concepts, descriptions and relationships)
  • Provide standard representations for subsets, language preferences and maps to other codes and classifications.

  • Are distributed as tab-delimited text files - which represent character content in accordance with the  Unicode UTF-8 specification;
  • Use SNOMED CT Identifiers as the permanent Identifier of released core components;

  • Support extensions to the International Release using namespaces allocated to licensees to denote the provenance of added components and to ensure Identifier uniqueness.