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The main reasons for adding descriptions in an extension are:

  • To translate SNOMED CT into another language
  • To add terms that are preferred or accepted within a local setting, for example
    • Common clinical terms that facilitate searching for concepts
    • Patient friendly terms
  • To support the creation of new concepts in the extension, which each require at least two descriptions



As depicted in Figure, a description in an extension may refer to any concept in the same extension (Extension B), any concept in a module upon which the extension modules depend (Extension A), or any concept in the International Edition.

Figure Descriptions can reference concepts in other modules on which the extension modules depend

Note that the green and orange triangles pointing to the purple circle represent a situation in which a description is added to an extension that describes an international concept. These extension descriptions supplement the descriptions that are already part of the International Edition.

Adding Descriptions for a New Concept

Descriptions in SNOMED CT are represented in a description file. At least two descriptions must be created for each new concept in an extension: 

  • A description of type | Fully specified name|  (FSN)
    • Note that all extension producers should create an unambiguous FSN in US English for each new concept. Additional FSNs may also be created to support other languages and dialects.
  • A description of type | Synonym| , in either English or an alternative language

The acceptability of new descriptions must be specified in a language reference set.

Adding Fully Specified Names

The following principles apply to adding FSNs in an extension.

  • There may be more than one active description with a typeId of | Fully specified name|  (FSN).
    • However, only one FSN should be marked as preferred for use in a given language or dialect by a specific Language Reference Set.
  • Every extension concept must have an unambiguous FSN in US English.
    • The US English FSN is the point of reference for the meaning of all concepts in the SNOMED CT International Edition.
    • The US English FSN is used to facilitate sharing and to resolve potential issues related to the interpretation of the meaning.
  • Extensions producers are permitted to create a FSN in each of their native languages.
    • This means that a non-English FSN may be marked as the preferred FSN in a specific language reference set in the extension.
    • Consequently, a concept may have more than one FSN. However, only one may be preferred in a specific language reference set. 
    • Where a concept has only one active description with a typeId of | Fully specified name|  across all language codes within a release, then that description can be assumed to be the FSN for all languages and dialects, and need not be explicitly included in every language reference set.

Adding Synonyms

  • Unlike FSNs, synonyms are not necessarily unique between concepts, as the same term can be used to describe more than one concept.
  • The preferred term is the synonym marked as preferred for use in the Language Reference Set for a given language or dialect.
    • There must be at least one description with a typeId of  | Synonym|  and an acceptabilityId value of | Preferred|  for each concept associated with a description in a given language reference set.

Adding Descriptions to an Existing Concept

When a description is created in an extension, as part of a translation or to provide a localized synonym for an existing concept, a new row should be added in the relevant language reference set to indicate whether the description is  | Preferred|  or | Acceptable|  in the given language or dialect. 


The table below provides a summary of the process to follow when adding new descriptions to an extension. 

File TypeProcess

A new row which represents the new description is added to the description file.

The attributes of the new description are set as follows:

  • id is set to a new descriptionId allocated within the extension namespace
  • effectiveTime is set to the date the extension will be published
  • active is set to 1 to indicate that the new description will be active at the time of publication
  • moduleId is set to the conceptId of a module that is managed by the extension producer
  • conceptId is set to the id of the concept to which this description applies
  • languageCode is set to the two character code of the language in which this term was authored
  • typeId is set to indicate the type of the description
  • term is set to the string of characters used to describe the given concept
  • caseSignificanceId is set to indicate the case significance of the term
Language Reference Set

A new row (or member) is added to each relevant language reference set.

The attributes of the new language reference set member are set as follows:

  • id is set to a unique automatically-generated UUID
  • effectiveTime is set to the date the extension will be published
  • active is set to 1 to indicate that the new member will be active at the tiem of publication
  • moduleId is set to the conceptId of a module that is managed by the extension producer
  • refsetId is set to the conceptId of the language reference set to which the member is added
  • referencedComponentId is set to the descriptionId of the new description
  • acceptability is set to indicate the acceptability of the new description in the relevant language or dialect
    • Value is either | Preferred|  or  | Acceptable|
    • Each concept may have only one preferred FSN and one preferred synonym in each language reference set

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