SNOMED Documentation Search

 Other Documents
Skip to end of metadata
Go to start of metadata

Current Version - Under Revision

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

Figure 12.2-1: Focus concepts and refinements

As illustrated by Figure 12.2-1, an expressionconsists of one or more conceptIds plus optional refinements. The refinementsmay include any number of attributes. Attributesare 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 conceptthat 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 conceptthat represents the appropriate value for this attribute. However, it may also be a nested expressionas shown in .

Error: Referenced caption id not found!

Captions on current page:
- Table: with ID: expression-nesting-
- Figure: with ID: concept-refinement
- Figure: with ID: nested-expression
- Figure: with ID: context-expression
 illustrates the potential for nesting of expressions and the naming conventions applied in this guide to distinguish different parts of an expressionat 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  refinementare a "nested expression" that consist of one or more "value concepts" optionally refined by a nested refinement. Expressionsmay 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 0expression

level 1expression

Anexpressionnested 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 expressionswhether or not they include context information. Figure 12.2-3 illustrates the specific features of an expressionthat includes a representation of context.

The "focus expression" of a context containing expressionis 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 wrappercontains 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