The logical design of an expression repository includes the entities required to hold the data relevant for an expression version.
As illustrated in Figure 5.2.1-1, an expression repository contains one or more expression versions.
Each expression version must contain the following data:
- Versioning data, to represent the time and substrate of the given version of the expression
- A Close-to-user form expression, to represent the expression as it was stated upon creation
Each expression version should contain the following data:
- An expression identifier, if this is required to uniquely identify the expression
- A Classifiable form expression, to enable the generation of the NNF expression
- A Necessary Normal Form expression, to support querying the expression
All SNOMED CT concepts referenced by expressions in the repository at a particular point in time should all be included, and active, in a specific versioned edition of SNOMED CT.
Figure 5.2.1-1: General expression repository design.
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