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

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

=20
des=
cendantOf =20
404684003 |Cl=
inical finding|=20

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

=20
des=
cendantOrSelfOf =20
73211009 |Diab=
etes mellitus|=20

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

=20
chi=
ldOf =20
404684003 |Cl=
inical finding|=20

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

=20
anc=
estorOf =20
40541001 |=
Acute pulmonary edema|=20

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

=20
anc=
estorOrSelfOf =20
40541001 |=
Acute pulmonary edema|=20

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

=20
par=
entOf =20
40541001 |=
Acute pulmonary edema|=20

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

=20
mem=
berOf =20
700043003 |Example problem list concepts reference set=
|=20

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

=20
ANY=
=20

=20
<=
;< =20
138875005 |S=
NOMED CT concept|<=
/span>=20

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

=20
*=20

=20
<=
;< *=20

=20
>=
;> *=20

=20
<=
; *=20

=20
<=
;! *=20

=20
>=
; *=20

=20
>=
;! *=20

=20
^&n=
bsp;*=20