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.

In this section we consider some of these simple examples.

Self

If no expression constraint operator or membership function is applied, the expression constraint is satisfied only by the specified concept. For example, the expression constraint below is satisfied only by the concept

	404684003 |

...

Clinical finding|

Please note that this expression constraint is equivalent to an expression that looks the same but is written in SNOMED CT Compositional Grammar.

Descendant

...

of 

Anchor
descendantOf descendantOf

A single 'less than' sign (i.e. "<") indicates that the expression constraint is satisfied by all descendants of the specified concept. The expression constraint below evaluates to the set of all subtypes (both direct children and transitive subtypes) of

	< 404684003 |

...

Clinical finding|

Using the long syntax, the above expression constraint may be represented as:

	descendantOf 404684003 |

...

Clinical finding|

The descendantOf function is primarily used on concepts, which serve as the 'grouper' of a set of values (e.g. 

Descendant or

...

Self of

Two consecutive 'less than' signs (i.e. "<<") indicates that the expression constraint is satisfied by all descendants of the specified concept plus the specified concept itself. The expression constraint below evaluates to the set of descendants of

	<< 73211009 |Diabetes mellitus|

Using the long syntax, the above expression constraint may be represented as:

	descendantOrSelfOf 73211009 |

...

Diabetes mellitus|

The descendantOrSelfOf function is primarily used for attribute values, which refer to a specific clinical value (e.g.

Child of

An exclamation mark directly followed by a A 'less than' sign directly followed by an exclamation mark (i.e. "<!") indicates  indicates that the expression constraint is satisfied by the set of immediate proximal children of the specified concept. The children of a concept are those concepts that are the source of a non-redundant

	<! 404684003|

...

Clinical finding|

Using the long syntax, the above expression constraint may be represented as:

	childOf 404684003|Clinical finding|

Please note that the childOf function may only be executed against a finite and pre-classified substrate, and that the results of this function are specific to the substrate used. The childOf function may also be applied to nested expression constraints (as discussed in  6.7 Nested Expression Constraints).

Child or Self of

Two consecutive 'less than' signs directly followed by an exclamation mark (i.e. "<<!") indicates that the expression constraint is satisfied by the set of proximal children of the specified concept plus the specified concept itself. The children of a concept are those concepts that are the source of a non-redundant 

	<<! 404684003|Clinical finding|

Using the long syntax, the above expression constraint may be represented as:

	childOrSelfOf 404684003|Clinical finding|

Please note that the childOrSelfOf function may only be executed against a finite and pre-classified substrate, and that the results of this function are specific to the substrate used. The childOrSelfOf function may also be applied to nested expression constraints (as discussed in  6.7 Nested Expression Constraints). 404684003 |clinical finding|

Ancestor of

A single 'greater than' sign (i.e. ">") indicates that the expression constraint is satisfied by all ancestors of the specified concept. The expression constraint below, using the brief syntax, evaluates to the set of all supertypes (both direct parents and transitive supertypes) of

	> 40541001 |

...

Acute pulmonary edema|

Using the long syntax, the above expression constraint may be represented as:

	ancestorOf 40541001 |

...

Acute pulmonary edema|

Please note that the ancestorOf function may also be applied to nested expression constraints (as discussed in  6.7 Nested Expression Constraints).

Ancestor or

...

Self of

Two consecutive 'greater than' signs (i.e. ">>") indicates that the expression constraint is satisfied by all ancestors of the specified concept plus the specified concept itself. The expression constraint below evaluates to the set of ancestors of

	>> 40541001|

...

Acute pulmonary edema|

Using the long syntax, the above expression constraint may be represented as:

	ancestorOrSelfOf 40541001 |

...

Acute pulmonary edema|

Please note that the ancestorOrSelfOf function may also be applied to nested expression constraints (as discussed in  6.7 Nested Expression Constraints).

Parent of

An exclamation mark directly followed by a A 'greater than' sign directly followed by an exclamation mark (i.e. ">!") indicates that the expression constraint is satisfied by the set of immediate proximal parents of the specified concept. The parents of a concept are those concepts that are the target of a non-redundant

	>! 40541001 |

...

Acute pulmonary edema|

Using the long syntax, the above expression constraint may be represented as:

	parentOf 40541001 |Acute pulmonary edema|

Please note that the parentOf function should only be executed against a finite and pre-classified substrate, and that the results of this function are specific to the substrate used. The parentOf function may also be applied to nested expression constraints (as discussed in  6.7 Nested Expression Constraints).

Parent or Self of

Two consecutive 'greater than' signs directly followed by an exclamation mark (i.e. ">>!") indicates that the expression constraint is satisfied by the set of proximal parents of the specified concept plus the specified concept itself. The parents of a concept are those concepts that are the target of a non-redundant 

	>>! 40541001

...

 |Acute pulmonary edema|

Using the long syntax, the above expression constraint may be represented as:

	parentOrSelfOf 40541001 |Acute pulmonary edema|

Please note that the parentOrSelfOf function should only be executed against a finite and pre-classified substrate, and that the results of this function are specific to the substrate used. The parentOrSelfOf function may also be applied to nested expression constraints (as discussed in  6.7 Nested Expression Constraints).

Member of

The memberOf function (by default) 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 is usually 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

	^ 700043003 |

...

Example problem list concepts reference set|

Using the long syntax the expression constraint is represented as:

	memberOf 700043003 |

...

Example problem list concepts reference set|

The expression constraints above both return the values in the referencedComponentId field of the given reference sets. However, it is also possible to specify one or more fields, whose values will be returned, by including the relevant field names is square brackets after the memberOf operator ("^" or "memberOf"). For example, the following expression constraint is equivalent to the brief syntax example above.

	^ [referencedComponentId] 700043003 |Example problem list concepts reference set|

The value of other fields can also be returned by an expression constraint

. For example, the following expression constraint will return the targetComponentId values (i.e. the 'Entire' anatomy concepts) from the 

	^ [targetComponentId] 734138000 |Anatomy structure and entire association reference set|

It is also possible to return the values of more than one field in a reference set (e.g. a pair or tuple of values).

For example, to return both the source and target of the 

	^ [referencedComponentId, mapTarget] 816210007 |SNOMED CT to MedDRA simple map reference set|

To return all the non-metadata fields of a referenceSet (i.e. the values of the referencedComponentId and additional fields), a wildcard (i.e. "*" in the brief syntax, and "*" or "Any" in the long syntax) can be used. For example, the following expression constraint will return the referencedComponentId, mapGroup, mapPriority, mapRule, mapAdvice, mapTarget and correlationId for each row of the 

	^ [*] 447562003 |ICD-10 complex map reference set|

For more information on the use of reference set field names in ECL, please refer to Appendix E - Reference Set Fields.

Please note that it is also possible to apply the memberOf function to an expression constraint that returns a set of concept-based reference set concepts. For more information, please refer to 6.7 Nested Expression Constraints.

And for information about applying filter constraints to reference set members, please refer to 6.10 Member Filters Please note that 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 the AAAAAA |allergen reference set|, which is defined as containing the members of the DDDDDD |drug allergen reference set| and the members of the FFFFFF |food allergen reference set|, then a row should be inserted into a query reference set with:
referencedComponentId = AAAAAA
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 "^ AAAAAA |allergen reference set|" will then be satisfied by both the concepts referenced by DDDDDD |drug allergen reference set| and the concepts referenced by FFFFFF |food allergen reference set|.

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.

	*

Using the long syntax, the above expression constraint may also be represented as:

	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:

	<< 138875005 |SNOMED CT concept|

However, some situations exist in which the concept

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

	*

	<< *

	>> *

The two expression constraint constraints below evaluates evaluate to all concepts in the substrate minus the root concept:

	< *

	<! *

And the two expression constraint constraints below evaluates evaluate to all non-leaf concepts in the substrate: 

	> *

	>! *

Finally, the expression constraint below evaluates to all concepts that are referenced by any reference set in the substrate:

	^ *

Alternate Identifier

If an alternate identifier exists for a concept, in an identifier scheme other than SNOMED CT, then this can be used to refer to that concept

 (see 4.2.4 Identifier File Specification). For example there may be SNOMED CT concept for "Type of hemoglobin in blood at point in time" with an alternate identifier with the scheme alias "LOINC" and the code "54486-6":

	LOINC#54486-6

The alternate identifier code can be surrounded by quotes.

The alternate identifier code can be surrounded by quotes.

The alternate identifier code can be surrounded by double quotes. Quoting may be necessary to ensure correct parsing of the constraint depending on the characters used in the code:

	LOINC#"54486-6"

Please note: ECL is always evaluated against SNOMED CT concepts. When you run a query using alternate identifiers from another code system only concepts that are in the SNOMED CT representation of that other code system will be returned. For example the descendants of a concept in the SNOMED CT version of a code system is likely to be different from the code system of the alternate identifier.