An Extension mechanism offers many advantages to developers, vendors, terminologists, national bodies and users.
Such a mechanism allows:
This structure also enables specialized Concepts and Descriptions within an Extension to be related to Concepts and Descriptions distributed as part of SNOMED CT.
The Concepts, Descriptions, Relationship and Reference Sets that form an Extension must be:
- Distinguishable from the main body of SNOMED CT, not only in the thesaurus, but also when stored in a patient record, query or decision support protocol;
- Distinguishable from other Extensions, in the same way as they are distinguishable from the main body of SNOMED CT ;
- Able to be distributed and processed in the same way as equivalent components from the main body of SNOMED CT without requiring specific adaptations of SNOMED-enabled applications.
The requirements for Extensions can be summarized as follows:
- Support for extra terminology components including Concepts, Descriptions, Relationships and Reference Sets:
- Globally unique identification of any terminology component that may be used outside the scope of a limited local environment:
- The mechanism allows several organizations to issue mutually exclusive Identifiers for components of their Extensions.
- To avoid the risk of misinterpretation, this mechanism is effective in various contexts including:
- Within the thesaurus;
- In patient records;
- In queries, decision-support protocols or knowledge bases.
- The mechanism indicates when Concepts have moved, or are expected to move, between an Extension and the International Release, or from one Extension to another.
- A shared understanding of the responsibility of an organization that creates an Extension and provides it for the use of other organizations. These responsibilities include: