Relationships may be added in an extension for various reasons including:
A SNOMED CT relationship involves three main concepts - the source concept, the destination concept, and the relationship type concept (also known as the 'attribute'). Each of the concepts in an extension relationship may belong to either a module from the extension itself, or a module upon which the extension depends (e.g. an international module).
When adding new relationships in an extension, the following principles apply:
This means that the sourceId of the relationship should refer to a concept in the extension.
In cases in which it is necessary to meet legitimate clinical needs or to correct identified clinical issues, an extension producer may add additional defining relationships to a concept which belongs to an International module (or a module on which the extension module depends). However, this should be done with extreme caution due to the potential impact on the classification results. If these situations arise, SNOMED International (or the module owner) must be notified.
In some cases, new attribute concepts may be added to an extension. While this is permitted, new attributes should be applied with caution, and concept model rules and editorial guidance should be clearly documented by the extension provider.
Attributes added in an extension can lead to inconsistent classification, where attributes overlap with or interact with attributes in the SNOMED International Edition. Furthermore, attributes created in an extension may not be well aligned with new attributes covering similar characteristics that may be included in future releases of the International Edition. Therefore, care should be exercised when adding attributes in an extension. In particular, the rationale for creating each new attribute should be well documented, with clear guidance on its consistent use. Ideally additions should also be made to the MRCM reference sets to capture the associated concept model rules in a machine processable way. If similar attributes are later added to the International Edition, the extension producer should plan to align with the International Edition as soon as possible.
|Cyclic Graph||Directed Acyclic Graph|
The table below provides a summary of the process to follow when adding a new relationship to an extension.
|Stated Axiom||A prerequisite for generating the relationships in the relationship file is that concepts have been authored and the defining properties stated and classified together with the SNOMED CT content it belongs to. Please see 184.108.40.206 Add Concept in an Extension.|
Once authoring is complete, the contents of the extension modules, together with every module on which these depend, are classified.
The resulting set of inferred relationships (i.e. the output of the classification process) is added to the Relationship file.
|A new row is added to the Relationship file for every inferred relationship that results from the classification process.|
The attributes of the inferred relationships are set as follows: