Maintaining reference sets starts already when the reference set is initially specified. The maintenance process includes both ensuring that the content of the reference set refers to active concepts in the release that the reference set depends upon. It also involves adding new content to the reference set, e.g. if additions to the dependee Release falls in scope of the reference set specification. Alignment of a reference set with the International Release, will be undertaken during the international release process. At which time a change report will be created for circulation, which gives details of both types of changes, in a format that can be circulated virtually to subject matter experts.
The tasks related to reference set changes, i.e. addition, inactivation or change of reference set members will typically include substituting a prior version of a subset with its more recent version. A simple example is if a reference set used to represent a value set used in a data entry interface – then the reference set may simply be replaced by the updated, new version of that reference set. But if the reference set is of more complex nature, e.g.. if it represents a map between SNOMED CT and a classification, and is used for quality monitoring, research, reimbursement etc. it might be necessary to go into more details about the implications of each of the changes to the reference set. Regardless of the type of reference set changes (change, addition or inactivation) it will in all cases have implications.
Addition of Reference Set
If new reference sets are added and implemented for data entry, then there may also be a need to develop queries to generate reports or views based on the new reference set data. Or, maybe an added reference set include rules to support enabling decision support, which then must be integrated. There may also be a need to create or update links between reference set members and communication protocols.
If a reference set is added then data entry protocols should be updated to link to this reference set where this is found appropriate. It could for example be if a reference set has been developed to function as a value set for cardiovascular diseases, then data entry protocols should link to this reference set in the data entry protocols used to capture cardiovascular diseases. The nature of such binding depends on the underlying information model of the protocol. Additionally, it will be important to update the storage models to include the captured information and store it appropriately. See Starter Guide Chapter 3. Using SNOMED CT in Clinical Information to learn about this topic.
Inactivation of Reference Set
A reference set may be inactivated in cases where an organization is no longer able or prepared to maintain it.
Inactivation of an entire reference set is done by inactivating the concept that identifies the reference set, and the relationship used to place the reference set in the subtype hierarchy.
Reference sets that are being actively used should not be inactivated without giving prior notice to allow remedial steps to be taken.
Any function that use a reference set that is no longer maintained will need updating. E.g. If reference sets are inactivated, which is used for data entry, it is important to determine how this is managed in the system. I.e it should be clarified if a new reference set should be defined, or if the inactivated reference set should be added in a local extension. It may also be, that a replacement reference set has already been defined.
Changes to Reference Set Members
The types of changes that can occur in a reference set include:
- Changes to reference set members
- Addition of reference set members
- Inactivation of reference set members
Additional information: TSG Guide Section 13.2 How to add, change or remove members of an existing reference set
Generally, the effect of changes to reference set members depend on the type of reference set and the way the reference set is used. In all cases, the changes should be managed properly, and therefore it is important to assess the extent to which the reference set changes affect the situation where the reference set is used, such as:
- Data entry. Changes to reference set members may require changes to existing data entry protocols.
- Data storage. Changes to reference set members may require pre-existing data to be migrated or processed in a particular way to ensure consistency.
- Data retrieval. Changes to reference set members may require existing queries to be revised to take account of the changes.
- Knowledge linkage. Changes to reference set members may require bindings to knowledge resources or decision support rules to be updated.
- Communications. Changes to reference set members may require communication specifications to be updated, and in particular to manage issues from cross-version communications.
Determine changes
One way of determine the changes to a reference set is by creating and comparing following two views of the reference set:
- SNAPSHOT view of the previous reference set release. A view which contains one version of every member released up to the time of the snapshot. The version of each member contained in a snapshot is the most recent version of that member at the time of the snapshot.
- DELTA view of the new reference set release. A view which contains only reference set member versions created since the previous reference set release. Each reference set member version in the DELTA view represents either a new reference set member or a change to an existing member.
With these two views it is possible to automatically identify whether a reference set member has been created, changed, reactivated or inactivated. The table below illustrate how to interpret the 'active' attribute, when you compare the delta view of the new release of the reference set with the snapshot view of the previous release of the reference set.
| Value of active column in the new release of the reference set (DELTA view) | ||||
|---|---|---|---|---|
| 0 | 1 | NOT PRESENT | ||
| Value of active column in previous release of the reference set (SNAPSHOT view) | 0 | Inactive member changed (not significant) | Member REACTIVATED | NO CHANGE |
| 1 | Member INACTIVATED | CHANGED member | NO CHANGE | |
| NOT PRESENT | n/a | NEW member | n/a | |
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