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Intensionally defined subsets are those which are automatically populated (or expanded) based on a machine processable query. For example, one might construct a subset of kidney disease codes using the results of the query "<< 90708001 |kidney disease|" (i.e. descendants or self of 90708001 |kidney disease|). The query used to define an intensional subset may utilize SNOMED CT's hierarchical relationships, attribute values, descriptions, and membership in other intensionally or extensionally defined subsets. For more information about SNOMED CT query languages, which may be used to define intensional subsets, please refer to section 9 Database Queries.

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Example

A subset containing types of 58437007 |tuberculosis of meninges| may be defined extensionally as follows:

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With the help of the SNOMED CT hierarchy (as shown in

Caption ref
Typefigure
IdTuberculosis
), this same subset can be defined intensionally as:

Scg expression
<< 58437007 |tuberculosis of meninges|

The expansion of an intensional subset defined using this query is the same as the extensionally defined subset shown above.

Footnote Macro

Expansion derived from SNOMED CT International Edition, dated 20170131.

Anchor_Ref403638465_Ref403638465 Anchor_Ref397604495_Ref397604495

Caption figure
IdTuberculosis
Tuberculosis of meninges concept sub-hierarchy

Using a lexical query, it is also possible to intensionally define a subset of 'tuberculosis of meninges' findings. However, the results of purely lexical queries are not as reliable. For example, using the query:

Scg expression
<< 404684003 |clinical finding| {{ term = ".tuberculosis.*meninges." }}


the following expansion can be calculated:

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As can be seen, the results of this lexical query only includes 3 of the possible 4 values from the previous subset. In other cases, lexical queries may incorrectly find concepts which are not appropriate to the subset. It is therefore recommended that lexical queries are avoided in the definition of intentional subsets. However, they do serve a useful purpose in identifying candidates for an otherwise manually crafted subset.

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Implementation

Defining Subsets in SNOMED CT

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