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.


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:

   900000000000455006 |Reference set|
900000000000521006 |Association type|
734138000 |Anatomy structure and entire association reference set|
734139008 |Anatomy structure and part association reference set|
900000000000522004 |Historical association|
                        /*  ... historical association types ...  */

Example Descriptors and Data

See Historical Association Reference Sets for an example of the reference set description and data representation in an association type reference set.