Historical Association Reference Sets are used to link concepts that have been inactivated to active concepts that represent an identical, similar or possible meaning of the inactivated concept.

Historical Association Reference Sets follow the release file specification documented in Association Reference Set with the inactive concept represented by the  referencedComponentId, the type of association represented by the  refsetId and the related active concept represented by the  targetComponentId.

The following subsections identify the metadata used to represent different types of historical associations.


The following metadata supports this  reference set:

Table Historical Association Reference Set names in the metadata hierarchy

   900000000000455006 |Reference set|
900000000000521006 |Association type|
900000000000522004 |Historical association|
900000000000523009 |POSSIBLY EQUIVALENT TO association reference set|
900000000000524003 |MOVED TO association reference set|
900000000000525002 |MOVED FROM association reference set|
900000000000526001 |REPLACED BY association reference set|
900000000000527005 |SAME AS association reference set|
900000000000528000 |WAS A association reference set|
900000000000529008 |SIMILAR TO association reference set|
900000000000530003 |ALTERNATIVE association reference set|
900000000000531004 |REFERS TO concept association reference set|

Historical Association Rules and Guidance

Each member of a  900000000000522004 | Historical association|  reference set represents a reference from an  inactive component to other equivalent or related  components that were current in the  Release Version in which that  component was inactivated.

Each  900000000000522004 | Historical association|  reference set represents a different type of association between the  components referred to by the  referencedComponentId and the  targetComponentId as shown in  Table

Table Association reference set types in the International Release of SNOMED CT

Association reference set


Applies to a concept that is ambiguous. The targetComponent is an active concept that represents one of the possible meanings of the inactive concept . Multiple rows are used to refer to each of the possible meanings of the ambiguous concept.

Applies to a component that has been moved to (or are pending a move to) another namespace. The targetComponent identifies the target namespace (not the new component ).

Applies to a component that has been moved to this namespace from another namespace. The targetComponent identifies the original componentIdentifier in its previous namespace.

Applies to an erroneous, obsolete and other inactive component for which there is a single active replacement. The targetComponent identifies the active component that replaces this component.

Applies to a component that is a duplicate. The targetComponent identifies the active component that this component duplicates.

Links an inactive classification concept such as "not otherwise specified" or "otherwise specified" with the active concept that was formerly its most proximal supertype.

(not used currently)

Links an inactive classification concept derived from ICD-9 Chapter XVI "Symptoms signs and ill-defined conditions" with the most similar active concept.

Applies to an inactive description which is inappropriate to the concept  it is directly linked to but instead should refer to the concept referenced by the targetComponent.

The  component identified by the  targetComponentId must be an instance of the same class of  component as the  component identified by the referencedComponentId for all |Historical association|  reference sets apart from the |REFERS TO  concept association  reference set|.

Reference Set Descriptor and Example Data

Notes on the tables used to show descriptors and examples

The reference set example tables on this page have been revised as follows to aid clarity and understanding:

  • The first four columns which are present in all release files are not shown. The omitted columns (ideffectiveTimeactivemoduleId) are used in the same way in all referenced sets to support identification, versioning and packaging. They do not directly affect the specific features of a particular reference set or reference set type.
  • Reference set columns that contain SNOMED CT identifiers are expanded to show details of the concept or description referenced by that identifier. In some cases, the term is shown in the same column using the expression syntax, in other cases an additional column with a name suffix '_term' has been added. In the standard reference set files only the identifier is present in the column and there is no added column for the term. When using reference sets, the term and other details of the component are looked up from the relevant component release files.

Descriptor Template

The tables below show examples of the descriptors for specific  reference sets that follow the  900000000000521006 | Association type reference set| pattern.

Table Refset Descriptor rows for the SAME AS association reference set

Example Data

The following table holds example entries for the  900000000000526001 | REPLACED BY association reference set| .

Table Sample content from


referencedComponentId (Association source component)

targetComponentId (Association target component)

Relevant References

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