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The figures in this section illustrate some terms used to describe different parts of an expression in the discussion of normal forms, the guidance on transforming expressions to normal forms and on testing subsumption and equivalence between expressions.

Figure 12.2-1: Focus concepts and refinements

As illustrated by Figure 12.2-1, an expression consists of one or more conceptIds plus optional refinements. The refinements may include any number of attributes. Attributes are expressed as name-value pairs and may apply independently or as part of a group.

The name part of the attribute value pair is a conceptId that refers to a concept that names the characteristic that is refined by this attribute. The value part of the attribute value pair is an expression. In simple cases, this is just a conceptId referring to a concept that represents the appropriate value for this attribute. However, it may also be a nested expression as shown in .

Table 12.2-1 illustrates the potential for nesting of expressions and the naming conventions applied in this guide to distinguish different parts of an expression at different levels. The top level of an expression  is referred to as the "focus expression". It consists of a set of one or more focus concepts and a refinement. The values of the attributes in the focus concept  refinement are a "nested expression" that consist of one or more "value concepts" optionally refined by a nested refinement. Expressions may be nested recursively so there may be further levels of "nested expressions" with "nested refinement". If it is necessary to distinguish the level of nesting, the following naming convention is applied.

Table 12.2-1: Expression Nesting

Level number

level 0 expression

level 1 expression

Nested expression

levelN expression

An expression nested inside a level ( N - 1) expression

 

Figure 12.2-2: Illustration of the names used to refer to parts of a nested expression

The general pattern shown in Figure 12.2-2 applies to all expressions whether or not they include context  information. Figure 12.2-3 illustrates the specific features of an expression that includes a representation of context.

The "focus expression" of a context containing expression is the context wrapper and may include a "context refinement" consisting of a set of context attributes:

In a normalized context expression, all context attributes are grouped. Each group in a normalized context wrapper contains a complete set of four context attributes [1 .

The value of the 246090004 |associated finding|or 363589002 |associated procedure|is a "nested expression" which is referred to as the "clinical kernel".

During some stages of processing, the "clinical kernel" is separated from the "nested expression". When separated from its context the "clinical kernel" is the "focus expression" of a context-free expression.

 

Figure 12.2-3: Illustration of the names used to refer to parts of an expression that represent context


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