2. General Information about Release Files

The standard format in which  SNOMED CThas 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 CTwas 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 RF2were:

• 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 setsto provide an extensible and versionable way to configure  SNOMED CT.Including support for subsets, maps, annotations, alternative hierarchies, etc.;

• Use of an added hierarchyto represent metadata about the structure of SNOMED CTitself.

In common with the earlier release format RF2specifies 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 Identifiersas the permanent Identifierof released core components;

• Support extensionsto the International Releaseusing namespacesallocated to licensees to denote the provenance of added components and to ensure Identifieruniqueness.