6.2 SCTID Representation

Each SCTID identifies a SNOMED CT component. The identifier itself does not contain information related to the meaning of a concept or description. This means it is not possible to infer anything about the meaning of a concept from the numeric value of the identifier or from the sequence of digits. The meaning of a concept can be determined from relationships to other concepts and from associated descriptions that include human readable terms.

The SCTID does however have a structure which includes valuable information about the nature and source of the identified component and the validity of the identifier. This structure supports the following features:

• Check-digit validation of the identifier.

  • The check-digit is the final digit in the decimal rendering of the identifier. This can be checked to minimize errors from transcription or incomplete copy-paste actions.

• Partitioning between identifiers for different types of SNOMED CT component.

  • A two-digit partition-identifier distinguishes the identifiers of different component types and prevents the same identifier from being allocated to both a concept and a description. As a result, when an SCTID is read from a record or other resource, it is possible to determine whether it represents a concept, a relationship or a description, before searching for the identified component.

• Namespaces to separate component identifiers originated by different organizations. 

  • Organizations are only permitted to issue identifiers which fall within a specified namespace of potential identifier values. This prevents collisions between identifiers issues by different organizations which would otherwise result in ambiguity and errors when sharing data.

  • There are two formats used for representing namespaces. 

    • Short format in which partition-identifiers are reserved for an organization which is permitted to issue any valid identifiers within the allocated partitions. The short format approach does not require a specific namespace-identifier and is only applicable to components originated and maintained by the SNOMED International as part of the International Release of SNOMED CT.

    • Long format in which the partition-identifier value indicates that a separate namespace-identifier is required to distinguish between components originated as part of an extension created by an appropriately authorized organization .