Current Version - Under Revision
An expression is a collection of references to one or more concepts . The expression consists one or more focus concepts and an optional refinement The focus concept and the names of the refining attributes are represented by references to SNOMED CT concepts . The value of a refining attribute is itself an expression and is structured in the same way. Thus nested expression can be used to refine the value of a refining attribute.
An expression represents an instance of the meaning defined by the defining relationships of the focus concepts as modified by the refinements The meaning of each refinement is expressed by an attribute name which names a property and an attribute-value which expresses the value of that property.
The refinement value may be a concept or expression that is a appropriate to the named attribute. The values that are appropriate to an attribute are specified by the Concept Model . In most cases, any subtype of a concept that is permitted as a value of an attribute is also permitted.
Figure 17. General Abstract Logical Model of a SNOMED CT expression