Store the Full Expression

With this approach, the full expression is stored in a single field, in the same way as the storage of single concept identifiers.

The following image illustrates the principle of storing the full expression in the expression repository.

Principles of storing the complete, full expression in the expression repository

The canonical version of the compositional grammar expression is recommended for the storage of the full expression, because this has a minimum of syntactic noise and specified sort order for the elements within the expression.

To use this approach, the health record must be able to record codes that are as long as the longest expression linked to one of the interface terms. The codes must also allow non-numeric values to be included, such as the colon and equal signs that are used in most expressions.

Some clinical systems, however, may have limits on the length or datatype of the codes that may be recorded in their health records. So, in these cases, a unique local identifier can be assigned to each expression, so that this shorter expression id can be stored in the health record in the place of the full expression (see Store Expression Identifier).

Terminology services

Storing the full expression in the EHR record requires the EHR to ensure that the stored expression represents a valid SNOMED CT expression. For this purpose, the following services may be required:

• Validate and Transform Expression (note, that for this purpose the CTU expression form of the expression should be used for data storage )

In conjunction to the EHR data storage, this process may also require the expression being added to an expression repository, which require the following services

• Lookup Expression

• Add Expression

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