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The use of description logic as the formal foundation of SNOMED CT allows the semantics of clinical concepts to be represented unambiguously. Description logic also enables logical deduction in which additional information can be inferred from the explicit statements in the terminology. Classification is the process in which the formally stated definitions of each concept are used to compute the subsumption hierarchies and defining properties of each concept.
With every each new release of SNOMED CT, two types of relationship files are distributed: the Stated Relationship file, containing the defining relationships stated by the terminology authors; and the Relationship file, containing the stated concept definitions are represented in the OWL Expression reference set, while the Relationship file, contains the full set of relationships that can be inferred using a classifier (excluding non-redundant
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OWL Expression Reference Set
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Inferred Relationships
Inferred relationships are derived from the set of stated defining relationshipsof
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Several semantically equivalent views may be inferred from the same set of stated relationships. However, the SNOMED CT Relationship file is distributed using an inferred view known as the Distribution Normal Form (DNF)
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In the necessary normal view (DNF):
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NNF) appropriate subtype and attribute relationships are created to represent non-redundant axioms that are necessarily true capable of being represented using the relationship file format.
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Some more advanced axioms (e.g.
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Example
This example is included to illustrate what happens during the classification process.
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