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Additional defining relationships may include
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Retaining Referential Integrity
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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. |
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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. |
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