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Reference sets are made available as release files that represent database tables. Each row of the table represents a member of the reference set 1 Each reference set member is represented using the set of attributes shown in the figure below. These common attributes include the four general identification and versioning attributes (shared with components) and two specific reference set attributes. This common set of attributes is sufficient to represent a versioned subset of SNOMED CT components.

As mentioned earlier, reference sets are used for purposes that go beyond subset representation. Different types of reference set are defined for each specific purpose. The definition of each reference set type specifies additional attributes and the way these are used. In these cases, each reference set member is represented by the combination of the common and type specific attributes. 

Figure 4.2-1: Attributes used in all types of SNOMED CT reference sets

Identification and Versioning Attributes

The reference sets have the same four initial attributes as the content components concepts, descriptions and relationships. These attributes are used to support identification, versioning and modularization.

Table 4.2-1: Overview and description of the general component attributes




The id attribute of the reference set uses the data type Universally Unique Identifier (UUID) to provide a globally unique identifier for each member of the reference set. This is different from the core Components of SNOMED CT, which use the data type SCTID.
The UUIDs are 128-bit unsigned integers. Their unique values are generated by widely available algorithms and not part of the SCTID namespace. This avoids the need to track issuing of identifiers for thousands of reference set rows that are needed for some reference sets.


The effectiveTime attribute uses the data type Time to specify the date on which the specific version of the component was released.


The active attribute uses the Boolean data type to specify whether or not the specific version of the component is active.


The moduleId attribute identifies the module in which the component is currently being maintained.

The three attributes, id, effectiveTime and active are used together to version each component.

Specific Reference Set Attributes

There are also two attributes that are shared by all reference set types, but not with the content components (concepts, descriptions and relationships). These attributes are called the refsetId and the referencedComponentId.

Table 4.2-2: Overview and description of the Specific reference set attributes. These attributes are present for all types of reference sets, but some reference sets have more attributes




The refsetId uses a SCTID to identify the reference set. The attribute refers to a concept and the concept's associated descriptions names the reference set. The concept is also a subtype to the concept that represents the type of reference set. One example of concept referenced by the refsetId is the concept 447566000 which description | Virtual medicinal product simple reference set | is the name of the reference set.


The referencedComponentId identifies a component referenced by the reference set. A reference set of type simple reference set represents a subset of SNOMED CT components. For this reference set type the referenced components are the subset members. One example of a component included in the 447566000 | Virtual medicinal product simple reference set| is | Warfarin sodium 5mg tablet |

Reference Set Member and  Referenced Component

The two terms "reference set member" and "referenced component" are sometimes used interchangeably, but when working with reference sets it is important to be aware of the distinct meaning of both of these terms, which should not be confused.

A reference set member is simply a single row in a specific reference set. Each member therefore includes the identifier of the member, the membership versioning information, the identifier of the component that is referenced by that row and all the other information that is recorded in a row of the reference set. In contrast, the 'referenced component' is the concept, description or relationship whose identifier appears in the referencedComponentId of the reference set.

Table 4.2-3: The referenced component is the value of the referencedComponentId attribute


Ref Notes
1 To be more precise, each row of a reference set table represents a version of a member of a reference set because, like SNOMED CT components, reference set members can be revised or inactivated by adding new versions to subsequent versions of a release file.

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