Generating SNOMED CT Identifiers

The following guidance is provided for organizations which have been issued namespace identifiers to create content in their own extension:

• Organizations must only generate new SCTIDs for components using a namespace identifier assigned to them by SNOMED International

• Organizations must have a mechanism in place to ensure that each SCTID is assigned only once. Generally, a single authority that generates item-identifiers in a sequential fashion for each type of component will achieve this goal.

• item-identifiers should not be generated so as to have meaning. They should be regarded as meaningless numbers. (Recall that an item identifier precedes the namespace identifier in an SCTID.)

Reference Set Members are identified with UUIDs instead of SCTIDs, so extension producers will also need the mechanism to generate UUIDs. UUID stands for Universally Unique Identifier, and each UUID is represented as a 128-bit number.

UUIDs are globally used to identify information in computer systems and they are for practical purposes unique, without depending on a central registration authority or coordination between the parties generating them. While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible.

Thus, anyone can create a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Information labeled with UUIDs by independent parties can, therefore, be later combined into a single database, or transmitted on the same channel, without needing to resolve conflicts between identifiers.

Several online platforms are available providing support for generating UUIDs, and for parsing their textual representation.

Prior to creating the components or reference sets in an extension, some preliminary steps must be completed. These tasks include:

1. Obtaining a namespace identifier from SNOMED International

   • A namespace identifier is required to generate component identifiers (SCTIDs)

2. Acquiring the appropriate tools to support the creation, management, and distrbution of the extension

   • Which tools, functionalities and services are required will depend on the content of the extension

   • For more information please refer to

   • Note that these tools will be used to complete the steps listed below

3. Creating module(s)

   • At least one module concept is required

   • Components and reference sets which belong to the extension are assigned to the approriate module

4. Specifying module dependencies

   • These dependencies are specified using the

   • This informs the consumers of the extension as to which additional modules are required to use/process the content of the extension

     • Note that some of these modules will come from other editions (such as the International Edition) and possibly, other extensions

The diagram below illustrates these key steps during the initial stage of extension creation.

It is important that extension producers understand that some aspects of authoring and managing an extension are complex and will benefit from appropriate tooling.

Editions should not be handcrafted or managed using documents, files or simple spreadsheets, as these are likely to lead to technical errors and inconsistencies. Extension content needs to be reviewed in relation to its dependencies on the International Edition (and any other dependencies) which makes manual management and validation of extension content an unsustainable practice. Tools are required to maintain SNOMED CT content appropriately and to initiate automatic checks which can prevent errors.

As part of authoring and preparing for a release, all extension producers need tools capable of managing RF2 release file structures and performing necessary validation checks. Managing of RF2 files includes a mechanism for creating components and reference sets. There may be additional functionality required but this will vary depending on the content of the extension. For example, some extension producers producing new clinical concepts will need to be able to classify their extension to validate the created content and create the inferred relationships (necessary normal view) based on the stated relationships in the extension. Extensions which are merely used to distribute a translated version of SNOMED CT, or locally defined reference sets that only reference international release content will not need this classifying functionality as these extensions will only include primitive, metadata concepts. Please see the section on Classifying an Edition for further information.

The table below summarizes the overall tooling considerations by category and services required. These are the tools required throughout the extension lifecycle including creation, management an distribution. Please note that this is not meant to be an exhaustive list, but instead summarize some of the key tools and services required.

Table: Extension tooling considerations