SNOMED CT has rich versioning mechanism that retains the full history of changes to every component and reference set member. As a result, it is possible to review the content of the terminology as it was at any time in the past and to make comparisons between two versions. In addition to tracking the state of the terminology at specific times in the past, the versioning mechanism also provides and indication of the reason for inactivation of each concept or description. In the case of concepts, there is also data linking inactive concepts to active concepts that may be used to replace them. Table 3.7.1-1 shows the terminology services required to access each of these different types of versioning data.
Table 3.7.1-1: Services Required to Access Details of Terminology Changes
| Practical Requirement | Status 1 | Required Terminology Services2 | Additional Terminology Service Dependencies3 |
| Enable the selection of SNOMED CT edition and the versions of that edition to be compared | REQUIRED | 4.1 Select Edition and Version | N/A |
Identify concepts that have been added, changed or inactivated between the specified versions. | REQUIRED | 4.9 Identify Changes to the Terminology
| 4.2 Get a Concept, Description or Relationship
|
| Get inactivation reason for each inactivated concept | REQUIRED |
| 4.10 Get Data from a Reference Set |
| Identify concepts that are candidates to replace each inactivated concept | REQUIRED |
| N/A |
| Identify descriptions that have been inactivated between the specified versions. | REQUIRED | 4.9 Identify Changes to the Terminology
| 4.2 Get a Concept, Description or Relationship
|
| Get inactivation reason for each inactive description | REQUIRED |
| N/A |
| Get changes to inferred definitions | OPTIONAL | 3.1.9 Identify Changes to the Terminology
4.4 Get Definition of a Concept
| 4.2 Get a Concept, Description or Relationship
|
| Get changes to stated definitions | OPTIONAL | 3.1.9 Identify Changes to the Terminology
4.4 Get Definition of a Concept
| 4.10 Get Data from a Reference Set
|
Footnotes
Applications designed to address this use case must support the practical requirements marked as Required. Support for the practical requirements marked as Optional is recommended as these provide enhanced functionality that may be required by some users.
In most cases, a reference to a subsection of 4 Terminology Service Types, implies a requirement for all services marked as Required in that subsection. However, where a reference is followed by a bulleted list, that list specifies the specific terminology services required. Some of the specific services listed as required for an Optional practical requirement may be marked as Recommended in the referenced subsection.
The Additional Terminology Service Dependencies column contains references to services on which a Required Terminology Service depends. This column does not restate dependencies on services listed as required service or additional dependencies for essential requirements listed in earlier rows. A full list of the dependencies of each terminology service is provided in the relevant subsection of 4 Terminology Service Types.
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