The simplest type of expression constraint contains a single con= cept optionally preceded by an expression constraint operator and/or member= ship function. Expression constraint operators (e.g. descendant of) travers= e the hierarchical relationships in SNOMED CT to return the set of concepts= that are directly or transitively connected to the focus concept. Membersh= ip functions return the set of concepts referenced by a reference set.

In this section we consider some of these simple examples.

If no expression constraint operator or membership function is applied, = the expression constraint is satisfied only by the specified concept. For e= xample, the expression constraint below is satisfied only by the concept 404684003 |Clin= ical finding|.

=20
=20
404684003 |Cl=
inical finding|=20

Please note that this expression constraint is equivalent to an expre=
ssion that looks the same but is written in=20
SNOMED CT Compositional Grammar.
A single 'less than' sign (i.e. "<") indicates that the expression co= nstraint is satisfied by all descendants of the specified concept. The expr= ession constraint below evaluates to the set of all subtypes (both direct c= hildren and transitive subtypes) of 404684003 |Clinical finding|, using the brief syntax.

=20
<=
; =20
404684003 |Cl=
inical finding|=20

Using the long syntax, the above expression constraint may be represe=
nted as:=20
=20
des=
cendantOf =20
404684003 |Cl=
inical finding|=20

The descendantOf function is primarily used on concepts, which serve =
as the 'grouper' of a set of values (e.g. =20
|Clinical finding (finding)|, =20
|Severities (qualifier value)|, =20
|Unit (qualifier value)|). The descendantOf function may also be=
applied to other concepts, or to nested expression constraints (as discuss=
ed in =20
6.7 Nested Ex=
pression Constraints).
Two consecutive 'less than' signs (i.e. "<<") indicates that the e= xpression constraint is satisfied by all descendants of the specified conce= pt plus the specified concept itself. The expression constraint below evalu= ates to the set of descendants of 73211009 <= span style=3D"color: #00ccff;" class=3D"sctpipe">|Diabetes mellitus|, plus the concept 73211009 |Diabetes mellitus= | = itself.

=20
<=
;< =20
73211009 |Diab=
etes mellitus|=20

Using the long syntax, the above expression constraint may be represe=
nted as:=20
=20
des=
cendantOrSelfOf =20
73211009 |Diab=
etes mellitus|=20

The descendantOrSelfOf function is primarily used for attribute value=
s, which refer to a specific clinical value (e.g.=20
73211009 |Diab=
etes mellitus|
,
73761001 |Colonoscop=
y|,=20
385055001 |Ta=
blet dose form|), but any specialization of this value is also acceptable. The des=
cendantOrSelfOf function may also be applied to other concepts, or to neste=
d expression constraints (as discussed in =20
6.7 Nested Ex=
pression Constraints).
A 'less than' sign directly followed by an exclamation mark=
(i.e. "<!") indicates that the expression constraint i=
s satisfied by the set of proximal children of the specified concept. The c=
hildren of a concept are those concepts that are the source of a non-redund=
ant 116680003 |is a| relati=
onship whose target is the given concept. The expression constraint below, =
represented using the brief syntax, evaluates to the set of immediate child=
ren of the concept

=20
<=
;! =20
404684003 |Cl=
inical finding|=20

Using the long syntax, the above expression constraint may be represe=
nted as:=20
=20
chi=
ldOf =20
404684003 |Cl=
inical finding|=20

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 a=
pplied to nested expression constraints (as discussed in =20
6.7 Nested Ex=
pression Constraints).
A single 'greater than' sign (i.e. ">") indicates that the expression= constraint is satisfied by all ancestors of the specified concept. The exp= ression constraint below, using the brief syntax, evaluates to the set of a= ll supertypes (both direct parents and transitive supertypes) of 40541001 |Acute pulm= onary edema|:

=20
>=
; =20
40541001 |=
Acute pulmonary edema|=20

Using the long syntax, the above expression constraint may be represe=
nted as:=20
=20
anc=
estorOf =20
40541001 |=
Acute pulmonary edema|=20

Please note that the ancestorOf function may also be applied to neste=
d expression constraints (as discussed in =20
6.7 Nested Ex=
pression Constraints).
Two consecutive 'greater than' signs (i.e. ">>") indicates that th= e expression constraint is satisfied by all ancestors of the specified conc= ept plus the specified concept itself. The expression constraint below eval= uates to the set of ancestors of 40541001 |Acute pulmonary edema|, plus the concept 40541001 |Acut= e pulmonary edema|= .

=20
>=
;> =20
40541001 |=
Acute pulmonary edema|=20

Using the long syntax, the above expression constraint may be represe=
nted as:=20
=20
anc=
estorOrSelfOf =20
40541001 |=
Acute pulmonary edema|=20

Please note that the ancestorOrSelfOf function may also be applied to=
nested expression constraints (as discussed in =20
6.7 Nested Ex=
pression Constraints).
A 'greater than' sign directly followed by an exclamat=
ion mark (i.e. ">!") indicates that the expression constrain=
t is satisfied by the set of proximal parents of the specified concept. The=
parents of a concept are those concepts that are the target of a non-redun=
dant |is a|&=
nbsp;relationship whose source is the given concept. The expression constra=
int below, represented using the brief syntax, evaluates to the set of imme=
diate parents of the concept 40541001 ~~|Acute pulmonary edema|~~.

=20
>=
;! =20
40541001 |=
Acute pulmonary edema|=20

Using the long syntax, the above expression constraint may be represe=
nted as:=20
=20
par=
entOf =20
40541001 |=
Acute pulmonary edema|=20

Please note that the parentOf function should only be executed agains=
t a finite and pre-classified substrate, and that the results of this funct=
ion are specific to the substrate used. The parentOf function may also be a=
pplied to nested expression constraints (as discussed in =20
6.7 Nested Ex=
pression Constraints).
The memberOf function evaluates to the set of concepts that are referenc= ed by the given reference set (i.e. the set of referencedComponentIds). Ple= ase note that this function may be applied only to reference sets whose ref= erenced components are concepts. The SNOMED CT Expression Constraint Langua= ge does not support use of the memberOf function on reference sets whose re= ferencedComponents are not concepts (i.e. descriptions or relationships).

The memberOf function is represented in the brief syntax using a 'caret'= character (i.e. "^") and is usually followed by a single concept id for a = concept-based reference set. For example, the following expression constrai= nt is satisfied by the set of concepts which are members of 700043003 |Example problem list concepts reference set|:

=20
^&n=
bsp;=20
700043003 |Example problem list concepts reference set=
|=20

Using the long syntax the expression constraint is represented as:=20
=20
mem=
berOf =20
700043003 |Example problem list concepts reference set=
|=20

Please note that it is also possible to apply the memberOf function t=
o an expression constraint that returns a set of concept-based reference se=
t concepts. For more information, please refer to=20
6.7 Nested Ex=
pression Constraints.
A single 'star' (i.e. "*") may be used in the place of a concept referen= ce to represent any concept in the substrate. The expression constraint bel= ow evaluates to the set of all concepts in the given substrate.

=20
*=20

Using the long syntax, the above expression constraint may also be re=
presented as:=20
=20
ANY=
=20

This wildcard character (or 'ANY' keyword) may be used anywhere withi=
n an expression constraint that a concept reference may be used. In many si=
tuations, the wildcard is equivalent to the following expression constraint=
:=20
=20
<=
;< =20
138875005 |S=
NOMED CT concept|<=
/span>=20

However, some situations exist in which the concept=20
138875005 |S=
NOMED CT concept|<=
/span> is not included in the substrate, and therefore cannot be u=
sed to determine the full set of concepts available. In other cases, the si=
ngle character wildcard may serve as a convenient shortcut for the longer e=
xpression constraint above.
Please note that the following three expression constraints evaluate to = the same set of concepts:

=20
*=20

=20
=20
<=
;< *=20

=20
=20
>=
;> *=20

The two expression constraints below evaluate to all concepts in the =
substrate minus the root concept:=20
=20
<=
; *=20

=20
=20
<=
;! *=20

And the two expression constraints below evaluate to all non-leaf con=
cepts in the substrate: =20
=20
>=
; *=20

=20
=20
>=
;! *=20

Finally, the expression constraint below evaluates to all concepts th=
at are referenced by any reference set in the substrate:=20
=20
^&n=
bsp;*=20