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. The following table lists the attributes used in the standard reference set format, and their purpose.

Reference Sets in an Extension

SNOMED CT is designed to allow the to be extended to meet national or local requirements. Amay contain components of various types includingand 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 Extensions 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 vs. Customized Reference Sets.