Release File Specification

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A  SNOMED CT International Release includes three distinct  release types.  Table 3.2-1 describes the release types and the differences between them.

Table 3.2-1: SNOMED CT Release Types

Release type

   Description

Full

A full release is a release type in which the release files contain every version of every component and reference set member ever released.

Snapshot

A snapshot release is a release type in which the release files contain only the most recent version of every component and reference set member released, as at the release date. 

Delta

A delta release is a release type in which the release files contain only rows that represent component versions and reference set member versions created since the previous release date. 

Notes

  • Each row in a delta release file represents either a new component or reference set member, or a change to an existing component or reference set member since the previous release date.
  • A delta release identifies differences between two versions of the same release package. 
  • A delta release added to the previous full release is identical to the full release of the new version.
  • The previous release date, on which a delta release is based, is usually the date of the most recent previous release. However, that may not always be the case. For example, where interim releases are made between two major releases there may be a combined delta release covering a period since a previous major release. 

Please note : 

  • Delta files have been removed from the SNOMED International release package, Managed Service Extensions and Derivative packages.  However a Delta Generation Tool is available for those who need it. The Delta Generation Tool allows users to create their own Delta between two fixed release dates - you can find it here: https://github.com/IHTSDO/delta-generator-tool/releases.

There are practical use cases for each  Release Type.

  • The full release allows access to all versions of the release. This is valuable for reviewing data entered using earlier versions and more generally supporting change management.
  • The snapshot release only includes the latest version of each component. This can be useful to optimize access to the current version but does not provide access to earlier versions.
  • The delta release only includes changes made between one version and the next. This provides a simple way to identify new and changed components to support change management and can also be used to update the previous version of the full release to the new version of the full release. However, the delta release cannot be used as a stand alone resource.

When considering which release type to use, it is worth noting that delta and snapshot views can be readily generated from the full release type. For this reason organizations that maintain  SNOMED CT extensions are required to provide the  full release type, while distribution of the other release types are optional.

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