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The design of SNOMED CT specifies that all components (concepts, descriptions and relationships) are identified using

Gloss
t SCTIDs

. As extensions follow the logical design, content within an extension is also identified using SCTIDs. Another key requirement is that each SCTID is universally unique. This means that extensions This is true for both components in the International Edition, and components in an extension. Extension producers therefore need a mechanism to ensure their SCTIDs will that their component identifiers are globally unique, and do not collide with the SCTIDs generated by other organizations or those generated by SNOMED International. This mechanism is called a . The SNOMED CT

Gloss
t namespace identifier

 provides this mechanism. The namespace identifier ensures that all components within an extension are properly and uniquely identified, both locally and globally.

Prior to creating an extension, each organization will need to must obtain a unique namespace identifier from SNOMED International (see http://snomed.org/changeadd). Once the namespace identifier has been identifier is issued, SNOMED International authorizes the allocated organization to generate SCTIDs within their allocated namespace . This means that organizations can create and maintain content in their own extension.The allocated to identify extension components. Each SNOMED CT namespace identifier is 7 digits in length and is included in all SCTIDs within the extension. This ensures global uniqueness of SCTIDs across the terminology. Content in the International edition does not include a namespace identifier in the SCTID. By including this 7 digit identifier in the appropriate position within an SCTID, and maintaining locally unique item identifiers, global uniqueness of SCTIDs can be ensured.

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Note: Information about applying for a namespace identifier can be found on the SNOMED International website : at http://snomed.org/changeadd

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The table below lists some examples of namespace identifiers and the organizations to which they are affiliated withallocated. These organizations include 

Gloss
t National Release Centers

 (or NRCs), local organizations, and commercial vendors. Note that this table is an excerpt from the SNOMED CT Namespace Registry as of October, 2017.

 below uses illustrates the SCTID associated with the concept

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structure of an extension SCTID using the concept 

Concept
t 5281000124103 |Persistent

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asthma|

from  from the 20170301 US edition Edition of SNOMED CT, 20170301. Components The structure of the SCTID have has been labeled and the namespace identifier is shown in red. Note that the spaces do not form part of the SCTID and have been added to improve readability.

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Info
icontitle false Caution
The namespace identifier used in an extension's SCTIDs When present in an SCTID, a namespace identifier should NOT be used as a the mechanism to associate a component with a particular determine which edition or extension . This association is made with a component belongs to. Instead, the moduleId attribute and is described in the is used for this purpose. For more information, see 4.2 Modules section.

Example

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For example, although Concept t 6811000087108 |CT guided biopsy of left lower limb|  includes the namespace identifier ... "1000087" (allocated to Canada Health Infoway) and the partition identifier "10", this concept ... belongs to the Concept ShowParts term t 900000000000207008 |SNOMED CT core module|  in the International Edition. The presence of the Canadian namespace identifier ... in this SCTID ... indicates that this concept was ... originally created by Canada Health Infoway and later promoted into the International Edition. ... For further information on content promotion, please refer to 5.7.1.3 Updating Extension. Overview Content Tools Apps {"serverDuration": 224, "requestCorrelationId": "efbbc31e04dd8345"}