Extensions Practical Guide

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changes.mady.by.user David Markwell

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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 

Concept
ShowPartsterm
t116680003 |is a|
relationships). It is important that extension producers are aware of the difference between these two files, and the fact that most Most consumers of the terminology SNOMED CT will use the Relationship file (containing the inferred relationships). The Stated Relationship file is OWL reference sets are primarily used by extension producers, but may also be used by terminology consumers that have access to a description logic classifier.

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Inferred relationships are derived from the set of 

Gloss
tOWL axioms
 in the OWL Expression Reference Set, by applying a consistent set of logical rules to the definition which take account of the definitions of related concepts.

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Note

Some more advanced axioms (e.g. 

Gloss
tgeneral class inclusions
)  can be represented in the OWL Expression Reference Set but cannot be represented in the Relationship File.

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