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As discussed in module dependencies, all extensions have modules which depend on the modules in the International Edition. Extensions may also have modules which depend on the modules from other extensions. Despite the dependencies between modules from various editions, all concepts in an extension must be a subtype of the root concept,
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Extension concepts must be a subtype of the SNOMED CT root concept | |
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The diagram illustrates how all concepts from Extension B are related to concepts in the International Edition. This is because the concept is either a direct child of a concept in the International Edition or because it is subsumed by concepts in the International Edition through subtype relationships defined by concepts in Extension A. |
The referential integrity of a concept in an extension is retained by the addition of at least one
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- Other concepts in the same extension module may be stated to be a subtypes of the new concept
- The organization responsible for another module that depends on this extension module may, in the future, state that some concepts in their module are subtypes of this new concept
- When a
is applied to the contents of the module (and the set of modules it depends upon), the defining relationships associated with a new fully defined concept may lead to additional subtype relationships being inferred. These inferred subtypes may be concepts in the extension module itself or in any module on which the extension module depends (including International Edition modules).Gloss PreSpace false t Description logic classifier - It is also possible (although caution is advised) that the creator of the new concept might state that the concept is a supertype of a concept in the International Edition or in another module on which the extension module depends.
- it is also possible (although caution is advised) that an extension producer might add a defining relationship to a concept in the International Edition (or in another module on which the extension module depends), and this new defining relationship may lead to a variety of new relationships (including subtype relationships) being inferred by a
.Gloss PreSpace false t Description logic classifier
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A good way to assess the impact of a change is to compare the
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The following 3 examples illustrate the impact of adding extension concepts as leaf concepts or intermediate concepts (after classification). The impact is considered in terms of how each addition effects subsumption testing using an example international concept 'G'.
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Impact on hierarchy | A primitive extension concept, which is created as a leaf concept, must always be a subtype of an international edition concept, and will not be classified as a supertype of an international concept. | ||||||
Impact on subsumption | The addition of this type of content does not impact subsumption testing of concepts in the international edition, because it will remain distal in the hierarchy to all International content after classification.
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Impact on hierarchy | The definition of a concept in an extension module may result in it being classified as an intermediate concept in the SNOMED CT polyhierarchy, as illustrated in the diagram above. This scenario results in the creation of two new inferred
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Impact on subsumption | This type of intermediate extension concept does not change the results of subsumption testing between international concepts. It does, however, have an impact on which relationships from the international edition are non-redundant in the extension edition. In this example, the inferred relationship G |is a| E becomes redundant when combined with the inferred relationships from the extension. Extension producers can handle this redundancy by:
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Impact on hierarchy | The definition of a concept in an extension module may result in it being classified as an intermediate concept in the SNOMED CT polyhierarchy, as illustrated in the diagram above. This scenario results in the creation of three new inferred | ||||||
Impact on subsumption | This type of intermediate extension concept may change the results of subsumption testing for particular international concepts, when used within the local edition. Extension producers should therefore exercise extreme caution when introducing this type of concept addition. When using the International Edition on its own, the concept G will not be treated as a subtype of the concept D. However, users of this example extension edition will see the international concept G as a subtype of the international concept D. This means that queries over international concepts stored in clinical data will lead to different results, depending on which edition is used. Therefore, intermediate concepts of this type may have serious consequences on the comparability and interoperability across SNOEMD CT Editions. |
Process
Concepts added to an extension are represented in a concept file. These concepts are part of a module which includes the namespace identifier assigned to the extension producer by SNOMED International. Each concept also requires additional components and reference set members to be defined. At a minimum, the following components and derivatives should be created:
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The table below provides a summary of the process to follow when adding a new concept to an extension.
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