SNOMED CT® Release Format 1 (RF1) Guide - ihtsdo

It is important to note that combining concepts at this level presumes that the result is intended to be a single
combined meaning which is subsumed by the meaning of the combined concepts. Furthermore, the same
refinements apply to the combined meaning of this set of concepts.
Some representational forms (e.g. HL7 version 3 Concept Descriptor data type) do not allow combinations
to be expressed in this way. However, it is possible to apply a simple logical transformation to create a
semantically identical view that can be conveyed in a syntax that supports a single focus concept with
refinements (see Figure 22 ).
Figure 22: An alternative view of an expression with two focus concepts
2.2.2.3.5. Expressions that include context
Structure and Content Guide | 55
Expressions may also explicitly represent the semantic context surrounding a finding or procedure. In these
cases, the finding or procedure is nested inside the context component of the expression. The outer layer of
the expression, which expresses the context, is sometimes referred to as the context wrapper. The nested
expression representing the finding or procedure is sometimes referred to as the "clinical kernel".
Figure 23 illustrates how the general concept 281666001 | family history of disorder | can be refined to
represent family history of a specific condition.
Figure 24 illustrates an alternative (computationally equivalent) representation of the same situation. In this
case the family history situation is itself represented by an expression.
Figure 23: Family history of a specific type of severe allergy to nuts as close-to-user form expression
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