In this section, we illustrate how description filters can be applied to expression constraints to further restrict the matching concepts.

Overview

Filter Description filter constraints provide 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 constraint criteria will be included in the set of matching concepts. Descriptions can be filtered based on their term, type, language, dialect, and acceptability in a given dialect. In the following sections, we explain each of these description filter criteria.

Term Filter

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 6.9 Concept Filter Constraints). 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.

* {{ D term = "heart att" }}

By default, term filters match using a word-prefix-any-order match technique. This means that each string value in the search term must match the start of a word in the concept's description term, but that these words may appear in any order. This word-prefix-any-order match technique can be explicitly specified in the term filter, using the keyword "match:" before the search term. For example, the following four expression constraints are equivalent, and are each satisfied only by diseases with a description term that includes both a word starting with "heart" and a word starting with "att" (in any order).

...

(<  404684003 |Clinical finding| :
         363698007 |Finding site|  = <<  39057004 |Pulmonary valve structure| , 
         116676008 |Associated morphology|  = <<  415582006 |Stenosis|) {{ term = "insufficiency" }}

Language Filter

Language filters enable an expression constraint to match on only those concepts with a matching description in a specified language. Language filters use the keyword "language", followed by a comparison operator (e.g. "=" or "!="), and the ISO 639-1 two-character language code (in upper or lowercase).

...

< 64572001 |Disease| {{ term = "hjärt", language = sv }} {{ term = "heart", language = en }}

Description Type Filter

Type filters enable an expression constraint to match on only those concepts with a matching description of a specified type. Type filters may either use the keyword "type" with the values "fsn", "syn" or "def", or may use the keyword "typeId" with a concept value that is 

...

< 56265001 |Heart disease| {{ term = "heart", typeId = (900000000000013009 |Synonym| 900000000000003001 |Fully specified name|) }}

Dialect Filter

Dialect filters enable an expression constraint to match on only those concepts with a matching description in a specified language reference set. Dialect filters may either use the keyword "dialect" with a value that represents a valid alias for a specific language reference set,  or may use the keyword "dialectId" with a concept value that is

...

< 64572001 |Disease| {{ term = "card", dialect = ( en-nhs-clinical en-nhs-pharmacy ) }}

Acceptability Filter

Acceptability filters enable an expression constraint to match on only those concepts with a matching description that has the specified acceptability in the specified language reference set. Acceptability filters must always be applied to a specified dialect. As such, they are represented by placing the required acceptability in brackets after the value of the dialect filter. Acceptabilities can be indicated using either one of the keywords below, or using a concept value that is 

...

< 64572001 |Disease| {{ term = "box", type = syn, dialect = ( en-gb en-nhs-clinical ) (prefer) }}

Filters with Negation

Filters can use negation in a number of ways. The simplest approach is to use the 'not equal to' comparison operator (e.g. "!=") before the value.

...