SNOMED CT Compositional Grammar may also be used to state the definition of precoordinated concepts. The introduction of definition status to this version of the language makes this usage more feasible. In particular, the definition of a fully defined concept uses an 'equivalent to' definition status to indicate that the expression is necessary and sufficient to define the clinical meaning of the concept. This is the same as giving the concept a definition status of 900000000000073002 | Defined| . The definition of a primitive concept uses a 'subtype of' definition status to indicate that the expression is necessary but not necessarily sufficient to define the clinical meaning of the concept. This is the same as giving the concept a definition status of 900000000000074008 | Primitive| .
For example, 31978002 | Fracture of tibia| (a fully defined precoordinated concept) can be defined using a compositional grammar expression as being 'equivalent to' an 428881005 | Injury of tibia| and a 46866001 | Fracture of lower limb| , with an 116676008 | Associated morphology| of 72704001 | Fracture| and a 363698007 | Finding site| of 12611008 | Bone structure of tibia| . This definition is shown below in Figure 1 using the SNOMED CT Diagramming Guidelines.
Figure 1: Definition of Precoordinated Concept
Please note that SNOMED CT expressions are used to represent a single clinical idea, rather than stating the equivalence between two clinical ideas. For this reason, a concept definition written as a SNOMED CT expression includes only the definition itself, without reference to the concept being defined. For an extension to the grammar which includes both the concept and its definition together, please refer to Appendix A.
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