A datatype representing a sequence for a unique Identifier encoded as a 128-bit integer. Their unique values are generated by widely available algorithms and are not part of the SCTID namespace. In SNOMED CT, the id attribute uses this datatype, for reference sets only. Their uniqueness avoids the need to track the issuing of identifiers for the thousands of refset rows that are needed in some implementations.
In SNOMED CT release files UUIDs are represented using a string following the standard canonical form. In this string form a UUID is represented by 32 hexadecimal digits, displayed in five groups separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters (32 digits and four hyphens).