Expression Constraint Language

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In this section, we illustrate how the set of matching concepts can be filtered using one or more attribute refinements.

Attributes

Adding an attribute refinement to an expression constraint restricts the set of valid clinical meanings to only those whose defining attributes satisfy the given refinement condition. Similarly to SNOMED CT Compositional Grammar, attribute refinements are placed after a 'colon' (i.e. ":") in the expression constraint.

The example below is satisfied only by the set of lung disorders, which have an associated morphology that is exactly equal to

Scg expression
ShowPartsterm
79654002|Edema|
.
Scg expression
ShowFormatblock
   < 19829001 |Disorder of lung|:
         116676008 |Associated morphology| = 79654002 |Edema|
Using the long syntax, the above expression is represented as:
Scg expression
ShowFormatblock
   descendantOf 19829001 |Disorder of lung| : 
         116676008 |Associated morphology| = 79654002 |Edema|
In many cases, however, the value of the matching attribute is allowed to be either the concept itself, or a descendant of that concept. In these cases, the descendantOrSelfOf operator is used prior to the concept representing the attribute value. For example, the expression constraint below (in brief and long syntaxes respectively) is satisfied only by the set of lung disorders, which have an associated morphology of
Scg expression
ShowPartsterm
79654002|Edema|
 or any descendant of
Scg expression
ShowPartsterm
79654002|Edema|
.
Scg expression
ShowFormatblock
   < 19829001 |Disorder of lung|: 
         116676008 |Associated morphology| = << 79654002 |Edema|
Scg expression
ShowFormatblock
   descendantOf 19829001 |Disorder of lung| : 
         116676008 |Associated morphology| = descendantOrSelfOf 79654002 |Edema|
When more than one attribute is defined in an expression constraint, the attributes are normally separated by a comma. A comma between two attributes indicates a conjunction and implies that both attribute conditions must be true. For example, the expression constraint below, written in brief syntax, is satisfied only by the set of clinical findings, which have both a finding site of
Scg expression
ShowPartsterm
39057004|Pulmonary valve structure|
 (or a subtype of
Scg expression
ShowPartsterm
39057004|Pulmonary valve structure|
) and an associated morphology of 'stenosis' (or a subtype of 'stenosis').
Scg expression
ShowFormatblock
   < 404684003 |Clinical finding|:
         363698007 |Finding site| = << 39057004 |Pulmonary valve structure|, 
         116676008 |Associated morphology| = << 415582006 |Stenosis|
Please note that attribute refinements may also be used when the focus concept is '*' (or ANY). The following expression constraint represents any concept that has a
Scg expression
246075003|Causative agent|
 attribute whose value is
Scg expression
387517004|Paracetamol|
.
Scg expression
ShowFormatblock
   * : 246075003 |Causative agent| = 387517004 |Paracetamol|
Using the long syntax, the above expression may also be represented as:
Scg expression
ShowFormatblock
   ANY : 246075003 |Causative agent| = 387517004 |Paracetamol|

Attribute Groups

Similarly to SNOMED CT compositional grammar, expression constraints use curly braces (i.e. "{..}") to indicate that a set of attributes should be grouped together in an attribute group. For example, the expression constraint below is satisfied only by the set of clinical findings with an associated morphology of 'stenosis' (or descendant) at the finding site 'pulmonary valve structure' (or descendant), and also with an associated morphology of 'hypertrophy' (or descendant) at the finding site 'right ventricular structure' (or descendant).

Scg expression
ShowFormatblock
   < 404684003 |Clinical finding|:
       { 363698007 |Finding site| = << 39057004 |Pulmonary valve structure|,
         116676008 |Associated morphology| = << 415582006 |Stenosis|},
       { 363698007 |Finding site| = << 53085002 |Right ventricular structure|, 
         116676008 |Associated morphology| = << 56246009 |Hypertrophy|}
Using the 'long syntax', the above expression constraint is represented as:
Scg expression
ShowFormatblock
   descendantOf 404684003 |Clinical finding|:
       { 363698007 |Finding site| = descendantOrSelfOf 39057004 |Pulmonary valve structure|,
         116676008 |Associated morphology| = descendantOrSelfOf 415582006 |Stenosis|},
       { 363698007 |Finding site| = descendantOrSelfOf 53085002 |Right ventricular structure|, 
         116676008 |Associated morphology| = descendantOrSelfOf 56246009 |Hypertrophy|}

Nested Attributes

Similarly to the SNOMED CT Compositional Grammar, it is also possible to nest expression constraints within an attribute value. Please note that when the attribute value is a simple expression constraint (as per the above examples), brackets are not required around the value. However, when the attribute value is either an expression constraint with a refinement, or a compound expression constraint with a binary operator, then brackets must be placed around the attribute value. For example, the following expression constraint represents the set of clinical findings which are associated with another clinical finding that has an associated morphology of 'infarct' (or subtype).

Scg expression
ShowFormatblock
   < 404684003 |Clinical finding|:
         47429007 |Associated with| = (< 404684003 |Clinical finding|: 
               116676008 |Associated morphology| = << 55641003 |Infarct|)
In this example, brackets are required around the nested attribute value "
Scg expression
< 404684003 |Clinical finding|: 116676008 |Associated morphology| = << 55641003 |Infarct|
".

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

Scg expression
ShowFormatblock
   descendantOf 404684003 |Clinical finding|:
         47429007 |Associated with| = (descendantOf 404684003 |Clinical finding|: 
               116676008 |Associated morphology| = descendantOrSelfOf 55641003 |Infarct| )

Attribute Operators

In some cases, an attribute concept has subtypes in the SNOMED CT hierarchy. Where this occurs, it is possible to indicate that an attribute condition may be satisfied by matching one of the subtypes of the given attribute. This is done using the 'descendantOf' or 'descendantOrSelfOf' operator directly before the attribute name concept. For example, the expression constraint below will not only match clinical findings that are associated with edema, but also those that are due to, after or caused by an edema. This result occurs because the

Scg expression
47429007|Associated with|
 attribute concept has three subtypes:
Scg expression
255234002|After|
,
Scg expression
246075003|Causative agent|
 and
Scg expression
42752001|Due to|
.
Scg expression
ShowFormatblock
   << 404684003 |Clinical finding|:
         << 47429007 |Associated with| = << 267038008 |Edema|
This expression constraint is represented in the long syntax as:
Scg expression
ShowFormatblock
   descendantOrSelfOf 404684003 |Clinical finding|:
         descendantOrSelfOf 47429007 |Associated with| = descendantOrSelfOf 267038008 |Edema|

Concrete Values

The revised SNOMED CT Compositional Grammar allows attributes to be given concrete values (e.g. Strings, Integers, Decimal). The SNOMED CT Expression Constraint Language supports the ability to compare these attribute values with a given concrete value.

When numeric concrete values (i.e. Integers and Decimals) are compared, a set of standard mathematical operators may be used. These mathematical operators are:

Operator

Name

=

Equals

!=

Not equals

<

Less than

<=

Less than or equals

>

Greater than

>=

Greater than or equals

Please note that the 'not equals' operator may alternatively be represented as "<>" and "not =" (case insensitive) in the long syntax. 

The following expression constraint

Footnote Macro

Please note that these examples are based on a hypothetical drug concept model, and is not intended to reflect any specific drug model. Concepts for which an identifier has not been assigned have been shown with an identifier of '111115'.

is satisfied only by amoxicillin capsules, whose strength is greater than or equal to 500 mg.
Scg expression
ShowFormatblock
   < 27658006 |Amoxicillin |:
         411116001 |Has dose form| = << 385049006 |Capsule|,
       { 111115 |Has basis of strength| = ( 111115 |Amoxicillin only|:
               111115 |Strength magnitude| >= #500, 111115 |Strength unit| = 258684004 |mg|)}
Please note that, as per SNOMED CT Compositional Grammar, integer and decimal values are preceded by a hash character (e.g. "#500"), while string values are surrounded by double quotes (e.g. "PANADOL").

To find those capsules that have a strength between 500 and 800 mg (inclusive), the following expression constraint may be used:

Scg expression
ShowFormatblock
   < 27658006 |Amoxicillin |:
         411116001 |Has dose form| = << 385049006 |Capsule|,
       { 111115 |Has basis of strength| = ( 111115 |Amoxicillin only|:
               111115 |Strength magnitude| >= #500, 111115 |Strength magnitude| <= #800, 111115 |Strength unit| = 258684004 |mg|)}
Concrete values of type string may also be included in an expression constraint, and compared using an 'equal to' (i.e. "=") or 'not equal to' (i.e. "!=") operator. The following expression constraint is satisfied only by products with a trade name equal to "PANADOL".
Scg expression
ShowFormatblock
   < 373873005 |Pharmaceutical / biologic product|:
         111115 |Trade name| = "PANADOL"

Reverse Attributes

In most cases, an attribute refinement is satisfied by those concepts, which are the source concept of a defining relationship whose target concept matches the attribute value. In some cases, however, it may be necessary to select the target concept of a relationship and constrain the source concept to a given attribute value. To achieve this, an expression constraint indicates that an attribute is to be constrained in the reverse order using a 'reverse flag'

Footnote Macro

It should be noted that using a reversed attribute joined by conjunction with a non-reversed attribute may lead to a nonsensical constraint (e.g. "<<a: {b=c, Rd=e}"). This is because the target concept of the reversed attribute must be matched with the source concept of the non-reversed attribute, which in turn must be the same as the source concept of the reversed attribute (being in the same attribute group). This would require the reversed attribute to be reflexive (i.e. the source and target concept to be the same).

. In the brief syntax, the reverse flag is represented by placing the name of the attribute being reversed inside a pair of round brackets, and preceding this with a capital letter 'R'.

For example, the expression constraint below finds the set of substances, which are active ingredients of 'TRIPHASIL tablet'.

Scg expression
ShowFormatblock
   < 105590001 |Substance|: 
         R 127489000 |Has active ingredient| = 111115 |TRIPHASIL tablet|
The above expression constraint is represented in the long syntax as:
Scg expression
ShowFormatblock
   descendantOf 105590001 |Substance|:
         reverseOf 127489000 |Has active ingredient| = 111115 |TRIPHASIL tablet|

Any Attribute Name and Value

A single 'star' (i.e. "*") may be used in the place of an attribute name to represent any attribute in the substrate. The expression constraint below evaluates to the set of clinical findings which have any attribute with a value of

Scg expression
79654002 |Edema|
.
Scg expression
ShowFormatblock
   < 404684003 |Clinical finding|: * = 79654002 |Edema|
Using the long syntax, the above expression constraint may also be represented as:
Scg expression
ShowFormatblock
   descendantOf 404684003 |Clinical finding|: ANY = 79654002 |Edema|
The 'star' symbol (i.e. "*") may also be used to represent any attribute value (either with or without refinement). The following expression constraint evaluates to the set of clinical findings which have an associated morphology (with any value).
Scg expression
ShowFormatblock
   < 404684003 |Clinical finding|: 116676008 |Associated morphology| = *
Using the long syntax, the above expression constraint may also be represented as:
Scg expression
ShowFormatblock
   descendantOf 404684003 |Clinical finding|: 116676008 |Associated morphology| = ANY
 

Display Footnotes Macro