Page History

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The SNOMED CT Composition Grammar was initially specified as part of the document "SNOMED Clinical Terms Abstract Logical Models and Representational Forms, External Draft for Comment Version". This version (v1) was used extensively as both a human readable and machine parsable syntax.

A revised version (v2.0 to v2.2) of this specification was adopted as an IHTSDO standard in 2010. This version followed the prior version in most details, with the following enhancements:

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In 2015, the original IHTSDO standard was revised (v2.3 and v2.3.1). The new specification is completely backwardly compatible with the prior standard, in that any expression written using the prior standard will necessarily conform to the new standard. However, two significant enhancements were made:

• Concrete values (e.g. integers, decimals and strings) are now permitted as attribute values.
• A definition status may now (optionally) be included at the start of an expression to indicate whether the clinical idea being expressed is 'equivalent to' or a 'subtype of' the expression.

In 2020, concrete attribute values were extended to permit booleans (v2.4).

These enhancements will be described and explained further within this guide.

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