Expression Constraint Language

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The simplest type of expression constraint contains a single concept optionally preceded by an expression constraint operator and/or membership function. Expression constraint operators (e.g. descendant of) traverse the hierarchical relationships in SNOMED CT to return the set of concepts that are directly or transitively connected to the focus concept. Membership functions return the set of concepts referenced by a particular reference set (or set of reference sets).

In this section we consider some of these simple examples.

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The memberOf function evaluates to the set of concepts that are referenced by the given reference set (i.e. the set of referencedComponentIds). Please note that this function may be applied only to reference sets whose referenced components are concepts. The SNOMED CT Expression Constraint language Language does not support use of the memberOf function on reference sets whose referencedComponents are not concepts (i.e. descriptions , or relationships or reference sets).

The memberOf function is represented in the brief syntax using a 'caret' character (i.e. "^") and must be immediately followed by a single concept id for a concept-based reference set. For example, the following expression constraint is satisfied by the set of concepts which are members of

Scg expression
ShowPartsterm
700043003|Example problem list concepts reference set|
:
Scg expression
Borderridge
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   ^ 700043003 |Example problem list concepts reference set |
Using the long syntax the expression constraint is represented as:
Scg expression
Borderridge
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   memberOf 700043003 |Example problem list concepts reference set |
Please note that it is also possible to represent the members of a reference set, which is itself composed of members of two or more other reference sets, an intensional definition should be created. For example, to refer to the members of theapply the memberOf function to an expression constraint that returns a set of reference set concepts. When this is done, the expression constraint to which the memberOf function is applied, must be enclosed in parentheses. For example, the following expression constraint is satisfied by the set of concepts which are members of any subtype of 
Scg expression
AAAAAA450973005 |AllergenGP/FP health issue reference set|
, which is defined as containing the members of the:
Scg expression
Borderridge
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   ^ (<450973005 |GP/FP health issueDDDDDD |Drug allergen reference set|
 and the members of the
)
The expression constraint above evaluates to the same set of concepts as applying the memberOf function to each individual subtype of 
Scg expression
FFFFFF450973005 |Food allergenGP/FP health issue reference set|
, then a row should be inserted into a query reference set with:and then taking the union of these sets. Therefore, when applied to the 20160731 international edition of SNOMED CT, the above expression constraint evaluates to the same set of concepts as the following expression constraint.
Scg expression
Borderridge
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   ^450990004|Adverse drug reactions reference  referencedComponentId = AAAAAA
and
Scg expression
Borderridge
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   query = ^ DDDDDD |Drug allergen reference set| OR ^ FFFFFF |Food allergen reference set|
(where AAAAAA, DDDDDD and FFFFFF are the concept identifiers of the respective reference sets).The expression constraint "
Scg expression
^ AAAAAA |Allergen reference set|
" will then be satisfied by both the concepts referenced by
Scg expression
DDDDDD |Drug allergen reference set|
 and the concepts referenced by
Scg expression
FFFFFF |Food allergen reference set|
.
set for GP/FP health issue| OR
   ^450989008|Allergies reference set for GP/FP health issue| OR
   ^450985002|Disorders and diseases reference set for GP/FP health issue| OR
   ^450988000|Family history reference set for GP/FP health issue| OR
   ^450991000|Processes and procedures reference set for GP/FP health issue| OR
   ^450986001|Results reference set for GP/FP health issue| OR
   ^450992007|Social history reference set for GP/FP health issue| OR
   ^450984003|Symptoms and signs reference set for GP/FP health issue|

Any

A single 'star' (i.e. "*") may be used in the place of a concept reference to represent any concept in the substrate. The expression constraint below evaluates to the set of all concepts in the given substrate.

Scg expression
Borderridge
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   *
Using the long syntax, the above expression constraint may also be represented as:
Scg expression
Borderridge
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   ANY
This wildcard character (or 'ANY' keyword) may be used anywhere within an expression constraint that a concept reference may be used. In many situations, the wildcard is equivalent to the following expression constraint:
Scg expression
Borderridge
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   << 138875005 |SNOMED CT concept|
However, some situations exist in which the concept
Scg expression
138875005 |SNOMED CT concept|
 is not included in the substrate, and therefore cannot be used to determine the full set of concepts available. In other cases, the single character wildcard may serve as a convenient shortcut for the longer expression constraint above.

Please note that the following three expression constraints evaluate to the same set of concepts:

Scg expression
Borderridge
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   *
Scg expression
Borderridge
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   << *
Scg expression
Borderridge
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   >> *
The two expression constraint constraints below evaluates evaluate to all concepts in the substrate minus the root concept:
Scg expression
Borderridge
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   < *
Scg expression
Borderridge
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   <! *
And the two expression constraint constraints below evaluates evaluate to all non-leaf concepts in the substrate:
Scg expression
Borderridge
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   > *
Scg expression
Borderridge
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   >! *
Finally, the expression constraint below evaluates to all concepts that are referenced by any reference set in the substrate:
Scg expression
Borderridge
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   ^ *