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An 900000000000521006 |Association type reference set|represents a set of unordered associations of a particular type between components.

Data structure

An Association reference set is a reference set used to represent associations between components. Its structure is shown in the following table.

Table 5.2.5-5: Association reference Set - Data structure


Data type


Part of Primary Key


A 128 bit unsigned Integer, uniquely identifying this reference set member.

Different versions of a reference set member share the same id but have different effectiveTime. This allows a reference set member to be modified or made inactive (i.e. removed from the active set) at a specified time.

NOYES (Full /Snapshot)

The inclusive date or time at which this version of the identified reference set member became the current version.

Note: In distribution files the effectiveTime should follow the short ISO date format (YYYYMMDD) and should not include the hours, minutes, seconds or timezone indicator.

The current version of this reference set member at time T is the version with the most recent effectiveTime prior to or equal to time T .


YES (Full)

Optional (Snapshot) 

The state of the identified reference set member as at the specified effectiveTime .

If active = 1 (true) the reference set member is part of the current version of the set, if active = 0 (false) the reference set member is not part of the current version of the set.


Identifies the SNOMED CT module that contains this reference set member as at the specified effectiveTime .

The value must be a subtype of 900000000000443000 |Module (core metadata concept)|within the metadata hierarchy.


Identifies the reference set to which this reference set member belongs.

In this case, a subtype descendant of: 900000000000521006 |Association type|


A reference to the SNOMED CT component to be included in the reference set.

The source component of the association.


The identifier of the target component of the association.

An inconsistency in this specification was resolved by the Modeling Advisory Group 2018-10-15 decision that this field should be mutable.



The following metadata supports this reference set:

Table 5.2.5-5: Association Reference Sets 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 5.2.5-3.

Table 5.2.5-3: 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 component Identifier 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 5.2.5-5: 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 5.2.5-5: Sample content from


referencedComponentId (Association source component)

targetComponentId (Association target component)

Relevant References