A subset is defined as
a set of members all of which are members of another set (from *set theory* in mathematics).

### Notes

- In SNOMED CT, the definition of
*subset*applies to SNOMED CT components as follows:A subset of SNOMED CT concepts is a set of concepts taken from a wider set of concepts.

A subset of SNOMED CT descriptions is a set of descriptions taken from a wider set of descriptions.

- The members of a subset can defined in one of two ways:
- Extensionally, by enumeration, with a simple reference set as the standard distribution format.
- Intensionally, using rules to determine inclusion, with a query reference set as the standard distribution format.

# Subset Example

The diagram below shows an example of a subset. The English vowels are a subset of the set of alphabet characters included in the English alphabet

Figure 2.1-1: Subset example

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