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Current Version - Under Revision


The purpose of RF2 is to provide a format that is flexible, unambiguous and useful. Its primary aim is to strengthen SNOMED CT by providing a format that is simple and stable, while enabling innovation through adaptations to cater for changing requirements.

This specification was developed by harmonizing proposals reviewed by the IHTSDO Enhanced Release Format Project Group, including:

Who should read this guide?

The intended audience for this guide includes technical professionals who are involved in the development and/or implementation of healthcare information systems that use SNOMED CT .

For detailed technical guidance on the existing Release Format , please consult the SNOMED CT Technical Reference Guide (TRG) and SNOMED CT Technical Implementation Guide (TIG), as well as other applicable technical documentation described in the Associated Documentation table.

For technical guidance on using Release Format 2 , please consult the " SNOMED CT Release Format 2 - Reference Set Specifications" and the " SNOMED CT Release Format 2 - Data Structures Specification" documents on the Collaborative site.

Associated Quality Measures

Although the definition of quality measures to monitor the implementation of this standard do not fall under the scope of this guide, they will be covered by the documentation covering the QA and Release process for the Workbench .

Summary of Changes

The RF2 introduces a number of new concepts and capabilities. These are summarized below, and described in more detail later in this guide:

  • Addition of an Identifier file to allow components to be identified by an arbitrary number of


    from an arbitrary number of


  • Addition of a module


    field to all components, enabling the source module in which each component is maintained to be identified, facilitating configuration management;
  • Modified handling of the




    properties of


    , for reduced complexity with increased utility;
  • Introduction of


    enumerations making enumerations within


    more easily extensible, self contained within the terminology (not dependent upon external documentation) and easily compatible across multiple


  • Addition of a

    description logic



    enumeration to the Relationship file to represent different

    Description Logic

    relationship types , for example - some, all, all-some, not-some etc.

A general extensibility design pattern has also been introduced, which allows specification of a number of Reference Set formats, to meet different use cases. In RF2 , reference sets :

  • Result from the combination of generic

    Reference Set

    data structures, a design pattern and the application of domain


    according to documented implementation guidelines;
  • Use a machine readable model (called a

    Reference Set

    descriptor) that defines the extended information pertinent to a specific

    Reference Set

  • Make use of


    enumerations for representing optional information to enable machine-readability and increased extensibility;
  • Apply the same history tracking and naming conventions as used elsewhere in



The RF2 enhancements all contribute to greater flexibility and more explicit and comprehensive version control than RF1 , and additionally introduce new features for configuration management. As a result, RF2 is expected to accommodate evolving collaborative requirements without a need for further fundamental change in the foreseeable future. Since change to the Release Format causes difficulty and incurs cost to content developers, implementers and release centers alike, the RF2 design is expected to result in long term (field) savings as well as improvement in product functionality and quality.

Timescales for change

It should be noted that there is a difference between the release schedule of RF1 / RF2 in official IHSTDO-supported International Releases , and the release schedule of RF1 / RF2 in Member NRC releases. It is entirely possible that RF1 will have a longer lifespan in Member NRC releases than in IHTSDO International Releases .

Actual timescales for migration of the International release to RF2 are provided under separate notices, and have not been included in this guide as they are likely to follow a different review cycle.