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

Overview

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 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, module, effectiveTime and active status.  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.

In the following sections, we explain each type 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.

...

< 64572001 |Disease| {{ term = "eye"}} {{ term = wild:"*itis"}}

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).

The expression constraint below matches only those diseases with a Swedish description containing the word prefix "hjärt" - e.g. Please note that filters apply only to the subexpression directly to the left of the filter. For example, the following expression constraint will apply the term filter to only the descendants or self of 

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

The expression constraint below matches only those diseases with a Swedish description containing the word prefix "hjärt" and an English description containing the word prefix "heart" - e.g. 

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

To apply a filter to a subexpression, which includes a refinement or binary operators, the subexpression must be enclosed in brackets. For example, the following expression constraint will find all the descendants of clinical finding, with a finding site that is a descendant or self of 

(<  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).

The expression constraint below matches only those diseases with a Swedish description containing the word prefix "hjärt" - e.g. 

< 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 

< 900000000000446008 |Description type|

. 

The following table lists the valid description type keywords in both the brief and full syntax, and their equivalent concept reference alternatives. Please note that the full syntax accepts both the brief and full syntax keywords. If additional description types are required, these must be specified in a filter using the 'typeId' keyword with the corresponding concept reference.

For example,  the expression constraint below matches all the subtypes of 

< 56265001 |Heart disease| {{ term = "heart", type = fsn }}

The following two expression constraints are equivalent, and both match only the subtypes of 

< 56265001 |Heart disease

< 64572001 |Disease| {{ term = "hjärt", language = svSV, type = syn }}

The expression constraint below matches only those diseases with a Swedish description containing the word prefix "hjärt" and an English description containing the word prefix "heart" - e.g. 

< 6457200156265001 |DiseaseHeart disease| {{ term = "hjärthjärta", language = sv, }} {{ term typeId = "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 

< 900000000000446008 |Description type|

. 

The following table lists the valid description type keywords in both the brief and full syntax, and their equivalent concept reference alternatives. Please note that the full syntax accepts both the brief and full syntax keywords. If additional description types are required, these must be specified in a filter using the 'typeId' keyword with the corresponding concept reference.

...

TypeId

Concept Reference

...

900000000000013009 |synonym| }}

The two equivalent expression constraints below match the subtypes of 

< 56265001 |Heart disease| {{ term = "heart", type = (syn fsn) }}

< 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

< 900000000000506000 |Language type reference set|

. Please refer to Appendix C - Dialect Aliases for a selection of valid dialect aliases for known language reference sets.

For example, the two equivalent expression constraints below will match all subtypes of 

< 64572001 |Disease| {{ dialect = en-au }}

< 64572001 |Disease| {{ dialectId = 32570271000036106 |Australian English language reference set| }}

The expression constraint below matches all diseases with a description in the New Zealand English language reference set that has a word starting with "cardio".

< 64572001 |Disease| {{ term = "cardio", dialect = en-nz }}

In some situations, multiple language reference sets need to be used together to identify an appropriate set of concepts. A filter constraint may include a list of dialects to specify that a matching description may belong to any of the given language reference sets. 

For example, the following expression constraint matches all diseases that have a description in either the en-nhs-clinical or en-nhs-pharmacy language reference sets, where that description contains a word starting with the prefix "card".

< 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 

< 900000000000511003 |Acceptability|

. The following table lists the valid acceptability keywords in both the brief and full syntax, and their equivalent concept reference alternatives. Please note that the full syntax accepts both the brief and full syntax keywords.

For example, the following two expression constraints both match all descendants of disease with a description that matches the word prefix 'box', has the type 'synonym', and has an acceptability of 'preferred' in the en-us language reference set. In other words, this expression constraint matches diseases with a US English preferred term that uses the word prefix 'box'.

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

< 64572001 |Disease| {{ term = "box", typeId = 900000000000013009 |Synonym|, dialect = en-us (900000000000548007 |Preferred|) }}

Multiple dialect filters may be used with different acceptabilities applied to each. For example, the expression constraint below matches on diseases, which have a synonym with word prefix "box" that is preferred in the en-nhs-clinical language reference set and is acceptable in the en-gb language reference set.

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

To support alternative acceptabilities in more than one language reference set, a dialect set can be used. For example, the following two equivalent expression constraints match on diseases, which have a synonym with word prefix "box" that is either preferred in the en-gb language reference set or preferred in the en-nhs-clinical language reference set.

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

< 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.

For example, the following expression constraint matches on For example,  the expression constraint below matches all the subtypes of 

< 56265001125605004 |HeartFracture of diseasebone| {{ term != "heartfracture", type = fsn }}syn, dialect = en-us (prefer)}}

If we remove the type and acceptability filters, as shown below, the remaining expression constraint matches on those The following two expression constraints are equivalent, and both match only the subtypes of 

...

...

...

< 56265001125605004 |HeartFracture of diseasebone| {{ term != "hjärtafracture", languagedialect = sv, typeId = 900000000000013009 |synonym| }}en-us}}

To find the set of concepts, for which all descriptions match some specified criteria, the expression constraint must use the MINUS operation to exclude concepts that have a non-matching description. For example, the expression constraint below matches all The two equivalent expression constraints below match the subtypes of 

< 56265001 |Heart disease 125605004 |Fracture of bone| MINUS < 125605004 |Fracture of bone| {{ term != "heart", type = (syn fsn) }}fracture"}}

This expression constraint can be simplified to the equivalent one below, using the wildcard character '*' (which represents any concept in the substrate).

< 56265001125605004 |HeartFracture of diseasebone| MINUS * {{ 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

< 900000000000506000 |Language type reference set|

. Please refer to Appendix C - Dialect Aliases for a selection of valid dialect aliases for known language reference sets.

For example, the two equivalent expression constraints below will match all subtypes of 

< 64572001 |Disease| {{ dialect = en-au }}

< 64572001 |Disease| {{ dialectId = 32570271000036106 |Australian English language reference set| }}

fracture"}}

Using a similar principle, the expression constraint below matches all concepts that do not have a preferred term specified in the en-nz language reference set.

* MINUS * {{ type = syn, dialect = en-nz (prefer) }}

Module Filter

Description module filters enable an expression constraint to match on only those concepts with a matching description that belongs to a specified module. Module filters use the keyword "moduleId" with a concept reference that is

< 900000000000443000 |Module|

.

For example, the expression constraint below matches all subtypes of 

< 64572001195967001 |DiseaseAsthma| {{ term = "cardio", dialect = en-nz }}

In some situations, multiple language reference sets need to be used together to identify an appropriate set of concepts. A filter constraint may include a list of dialects to specify that a matching description may belong to any of the given language reference sets. 

{{ D moduleId = 731000124108 |US National Library of Medicine maintained module| }}

And the expression constraint below matches all subtypes of 

< 64572001404684003 |DiseaseClinical finding| {{ D termtype = "card"def, dialectmoduleId = 900000000000207008 ( en-nhs-clinical en-nhs-pharmacy )|SNOMED CT core module| }}

...

Effective Time Filter

Acceptability Description effective time 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 

< 900000000000511003 |Acceptability|

. The following table lists the valid acceptability keywords in both the brief and full syntax, and their equivalent concept reference alternatives. Please note that the full syntax accepts both the brief and full syntax keywords.

...

AcceptabilityId

Concept Reference

...

description that has an effectiveTime matching the specified criteria. Effective time filters may use any of the date comparison operators shown below:

Please note that the value of an effective time filter (if present) must be a 8 digit date, formatted according to ISO 8601's basic calendar date format (i.e. YYYYMMDD). If the effectiveTime of the description in the substrate includes a time and/or time zone designator, these should be ignored when performing the comparison.

For example, the following expression constraint matches all subtypes of 

< 64572001125605004 |DiseaseFracture of bone| {{ D termeffectiveTime = "box", type = syn, dialect = en-us (prefer) }}"20210131" }}

And the following expression constraint matches all subtypes of 

< 64572001125605004 |DiseaseFracture of bone| {{ term = "box", typeId = 900000000000013009 |Synonym|, dialect = en-us (900000000000548007 |Preferred|) }}D effectiveTime != "20210131" }}

Similarly, greater than, less than, greater than or equals and less than or equals operators may be used in an effectiveTime filter. For example, the following expression constraint matches all subtypes of 

< 125605004 |Fracture 64572001of bone|Disease| {{ D termeffectiveTime >= "box20190731", type = syn, dialect = en-nhs-clinical (prefer), dialect = en-gb (accept) }}}}

And the following expression constraint matches all subtypes of 

< 64572001125605004 |DiseaseFracture of bone| {{ D termeffectiveTime <= "box", type = syn, dialect = ( en-gb (prefer) en-nhs-clinical (prefer) ) }}

< 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.

20190731" }}

The effectiveTime filter can also use sets of effective times. For example, the following expression constraint matches all subtypes of 

< 125605004 |Fracture of bone| {{ D effectiveTime = ("20190131" "20190731" "20200131" "20200731" }}

And the expression constraint below matches all subtypes of 

< 125605004 |Fracture of bone| {{ termD effectiveTime != ("fracture20190131", type = syn, dialect = en-us (prefer)}}"20190731" "20200131" "20200731" }}

To match concepts with unpublished descriptions, to which an effectiveTime has not been assigned, an effectiveTime value of "" can be used. For example, the following expression constraint matches all subtypes of 

< 125605004 |Fracture of bone| {{ D termeffectiveTime != "fracture", dialect = en-us}}

Please note that description effectiveTime filters, which use the comparison operators "<" and ">", will not match any descriptions with an effectiveTime = "".

Active Filter

Description active filters enable an expression constraint to match on only those concepts with a description that has a matching active status. Descriptions are either active (i.e. active = 1 or active = "true") or inactive (i.e. active = 0 or active = "false"). By default, only active descriptions are included in the substrate.

For example, the following expression constraints return all concepts in the International Patient Summary reference set, which have an active descriptionTo find the set of concepts, for which all descriptions match some specified criteria, the expression constraint must use the MINUS operation to exclude concepts that have a non-matching description. For example, the expression constraint below matches all subtypes of 

<^ 125605004816080008 |FractureInternational ofPatient boneSummary| MINUS < 125605004 |Fracture of bone{{ D active = 1 }}

^ 816080008 |International Patient Summary| {{ termD active != true "fracture"}}

This expression constraint can be simplified to the equivalent one below, using the wildcard character '*' (which represents any concept in the substrate)And the following expression constraints return all concepts in the International Patient Summary reference set, which have an inactive description.

<^ 125605004816080008 |FractureInternational ofPatient boneSummary| MINUS * {{ D termactive != "fracture"0 }}

Using a similar principle, the expression constraint below matches all concepts that do not have a preferred term specified in the en-nz language reference set.

* MINUS *^ 816080008 |International Patient Summary| {{ typeD =active syn, dialect = en-nz (prefer)false }}