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A representation of a SNOMED CT expression in which none of the referenced concepts are fully defined and where there is no redundancy or duplication of meaning.


  1. Normal forms can be used to determine equivalence and subsumption between expressions and thus assist with selective retrieval.
  2. Any SNOMED CT expression can be transformed to its normal form by replacing each reference to a fully defined concept with a nested expression representing the definition of that concept. Transformation rules then resolve redundancies, which may arise from expanding fully defined concepts, by removing less specific attribute values.