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Description filter constraints provide the ability the ability to limit the set of concepts, that satisfy a given expression constraint, based on the descriptions associated with each concept. Only concepts that have at least one matching description for each filter criteria will be included in the set of matching concepts. Descriptions can be filtered based on their term, type, language, dialect, acceptability in a given dialect, module, effectiveTime and , active status and description identifier.  Description filters are specified inside double curly braces, and optionally being with the letter "D". Any filter that does not specify its type is, by default, assumed to be a description filter.

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Term filters enable an expression constraint to match on only those concepts with an associated description whose term matches the given search term. For example, the following expression constraint is satisfied by SNOMED CT concepts with a description matching the search terms "heart" and "att". This expression constraint works like a term search performed in a SNOMED CT browser. Please note that the "D" (either upper or lower case) at the start of the filter indicates that this is a description filter constraint, rather than a concept filter constraint (see see 6.9 Concept Filter ConstraintsFilters). If the type of a filter constraint is not specified (as in most of the examples below), then it is assumed that the constraint is a description constraint.

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^ 816080008 |International Patient Summary| {{ D active = false }}

Description Id Filter

Description id filters enable an expression constraint to match on only those concepts with a description that has a matching description identifier. For example, the following expression constraint matches any concept, which has an associated description with the identifier "3032638017". The only concept that matches this expression constraint is

* {{ D id = 3032638017 }}

Description id filters can also be applied to other expression constraints, to check whether the concept with the matching description id is in a given set of concepts. For example, the following expression constraint will match any descendant of

< 195967001 |Asthma (disorder)| {{ D id = 3032638017 }}

Description id filters may also include a set of description identifiers. The following expression constraint will match any descendant of

< 195967001 |Asthma (disorder)| {{ D id = (1208972017 2674140012 3043971012) }}

Please note that inactive concepts can have active descriptions, so the description id filter can be applied after inactive concepts are added to the query results via a history supplement. For example, the following expression constraint matches any descendant of the concept

(< 195967001 |Asthma (disorder)| {{+HISTORY}}) {{ D id = 264553015 }}

For more information on history supplements, please refer to 6.11 History Supplements.