Hence, reference sets are a mechanism that can be used to represent subsets and value sets of SNOMED CT components. However, they can also be used for many other purposes, including those summarized in 3.2. Use Cases. The following table lists the attributes used in the standard reference set format, and their purpose.

Standard reference set format


 General versioning information





Reference set identifier


Component reference


  … attribute-n>

Additional information depending on reference set type

Reference Sets in an Extension

SNOMED CT is designed to allow the to be extended to meet national or local requirements. A may contain components of various types including and derivatives including Since the International Release and extensions share a common structure, the same application software can be used to enter, store and process information from different extensions. Extensions can also be shared without requiring additional software procurement or development.  Most E xtensions are managed by  Members or Affiliates of SNOMED International.

Reference sets authored in an extension use the same common format as those in the International Edition. This makes it easier to use the same software to create, maintain and share extension reference sets, as used by international reference sets. The reference set format can also be customized in an extension using a standardized customization approach, as explained in section 4.3. Pre-defined and Customized Reference Sets.