6.5 Expression With Nested Refinements

It is also possible to nest expressions, one inside the other. Any valid expression may be enclosed in a pair of brackets, and included as the value of an attribute in another expression. For example, the following expression describes a medication product that has a single dose form, which is both a spray and a suspension:
373873005 |pharmaceutical / biologic product|:
411116001 |has dose form| =
(421720008 |spray dose form| + 7946007 |drug suspension|)
In the example above, note the use of round brackets (i.e. "( )") to identify a nested expression, as opposed to braces (i.e. "{ }"), which is used to identify attribute groups.
The following examples show how complex expressions may be build up from simple ones, a layer at a time. This first expression describes a left hip structure:
24136001 |hip joint structure|:
272741003 |laterality| = 7771000 |left|
This next expression uses the "left hip" expression above to describe a procedure to replace it:
397956004 |prosthetic arthroplasty of the hip|:
363704007 |procedure site| = (24136001 |hip joint structure|: 
272741003 |laterality| = 7771000 |left|)
Applying a further grouped refinement to the above describes a procedure to replace a left hip by inserting a prosthesis. Note that this example mixes an ungrouped qualification and a grouped qualification. Where this is done, the canonical representation of the expression includes all ungrouped attributes before the grouped ones (section 7.8.2.4.4.4.2 of the SNOMED CT Technical Implementation Guide [6]). Please also note that in the previous version of this standard a comma was not permitted between the last ungrouped attribute and the first attribute group – however this comma is now optional to avoid unexpected syntax errors.
397956004 |prosthetic arthroplasty of the hip|: 
405814001 |procedure site - indirect| = (24136001 |hip joint structure|: 
272741003 |laterality| = 7771000 |left|),
{ 363699004 |direct device| = 304120007 |total hip replacement prosthesis|,
260686004 |method| = 425362007|surgical insertion - action|}
Finally, the above expression may be included within a contextual wrapper, to describe a procedure that has been performed on a patient to replace a left hip by inserting a prosthesis.
243796009 |situation with explicit context|:
{ 408730004 |procedure context| = 385658003 |done|, 
408731000 |temporal context| = 410512000 |current or specified|,
408732007 |subject relationship context| = 410604004 |subject of record|, 
363589002 |associated procedure| =
( 397956004 |prosthetic arthroplasty of the hip|: 
405814001 |procedure site - indirect| = (24136001 |hip joint structure|:
272741003 |laterality| = 7771000 |left|)
{ 363699004 |direct device| = 304120007 |total hip replacement prosthesis|,
260686004 |method| = 425362007|surgical insertion - action|}) }