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:

Cyclic GraphDirected Acyclic Graph




The table below provides a summary of the process to follow when adding a new relationship to an extension.

File TypeProcess
Stated AxiomA 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 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:

  • id is set to a new relationship identifier allocated within the extension namespace.
  • effectiveTime is set to the date the extension will be published
  • active is set to '1' to indicate that the new relationship will be active at the time of publication
  • moduleId is set to identify a module concept from the extension
  • sourceId is set to the source concept in the relationship. This will usually belong to the extension module.
  • destinationId is set to the destination concept in the relationship
  • relationshipGroup is set to a number that indicates which relationships with the same sourceId are logically grouped together
  • typeId is set to an attribute concept that represents the type of the relationship
  • characteristicTypeId is usually set to 900000000000011006 |Inferred relationship|
  • modifierId is usually set to 900000000000451002 |Existential restriction modifier|