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 =  ws [definitionStatus ws] subExpression ws

An expression often consists only of a subExpression. However, in some cases a definition status is needed to state whether the clinical meaning being represented is equivalent to or a subtype of the subExpression. If no definition status is included, the clinical meaning being represented is assumed to be 'equivalent to' the subExpression.

subExpression = focusConcept [ws ":" ws 

]

A subexpression consists of one or more focus concepts, optionally followed by a refinement. The meaning of the 

 is a 

 of all the focus

 constrained by the refinement. Note that where there is a requirement for multiple separately qualified 

 to be present these are expressed in 

 within a 

 of a general 

 such as " 

 ".

definitionStatus = equivalentTo / subtypeOf

The definition status states whether the clinical meaning being expressed is equivalent to or a subtype of the given expression representation.

equivalentTo = "==="

A definition status of equivalentTo (i.e. "===") indicates that the clinical meaning being represented is semantically equivalent to the given expression. If no definition status is included in the expression, this definition status is assumed.

subtypeOf = "<<<"

A definition status of subtypeOf (i.e. "<<<") indicates that the clinical meaning being represented is a semantic subtype (or subclass) of the given expression.

focusConcept =

Reference *(ws "+" ws conceptReference)

A focusConcept consists of one or more concept references separated by 'plus' signs.

Reference = conceptId [ws " {*}

 " ws  term ws " 

{*} "]

A 

Reference is represented by a ConceptId optionally followed by a  term enclosed by a pair of "

" characters. Whitespace before or after the ConceptId is ignored as is any whitespace between the initial "

" characters and the first non-whitespace character in the  term or between the last non-whitespace character and before second "

" character.

conceptId = sctId

The ConceptId must be a valid 

 for a 

. The initial digit may not be zero. The smallest number of digits is six, and the maximum is 18.

term = nonwsNonPipe *( *SP nonwsNonPipe )

The  term must be the  term from any 

 that is associated with the 

 identified by the preceding 

. For example, the  term could be the preferred 

for a given dialect. The  term may include valid  UTF-8 characters except for the pipe "

" character. The  term begins with the first non-whitespace character following the starting "

" character and ends with the last non-whitespace character preceding the next "

" character.

 = (attributeSet / attributeGroup) *( ws ["," ws] attributeGroup )

A 

 contains all the grouped and ungrouped attributes that refine the meaning of the containing 

.

attributeGroup = "{" ws attributeSet ws "}"

An 

 contains a collection of attributes that operate together as part of the 

 of the containing 

.

attributeSet = attribute ( ws " ,{*} " ws attribute )

An attribute set contains one or more 

-value pairs, separated by commas.

attribute = attributeName ws "=" ws attributeValue

An 

-value pair expressing a single 

 of the containing 

.

attributeName = conceptReference

The attribute name is the name of an attribute (or relationship type) to which a value is applied to refine the meaning of a containing 

. The 

 is represented in the same way as other concept references.

attributeValue = expressionValue / QM stringValue QM / "#" numericValue

An attribute value is either an expression, a string-based concrete value enclosed in quotation marks, or a numeric concrete value (i.e. integer or decimal) preceded by a "#".

expressionValue = 

Reference / "(" ws subExpression ws ")"

An expression value is either a single concept reference without brackets, or a more complex expression enclosed in round brackets.

stringValue = 1*(anyNonEscapedChar / escapedChar)

A string value includes one or more printable ASCII characters (these are also valid UTF8 characters encoded as one octet) and/or UTF8 characters encoded as 2- 3- or 4-octet sequences. Quotes and backslash characters must be preceded by the escape character ("\").

numericValue = decimalValue / integerValue

A numeric value is either an integer or a decimal.

integerValue = (["-"/"+"] digitNonZero *digit ) / zero

An integer may be positive, negative or zero. Positive integers optionally start with a plus sign ("+"), followed by a non-zero digit followed by zero to many additional digits. Negative integers begin with a minus sign ("-") followed by a non-zero digit and zero to many additional digits.

decimalValue = integerValue "." 1*digit

A decimal value starts with an integer. This is followed by a decimal point and one to many digits.

sctId = digitNonZero 5*17( digit )

A SNOMED CT id is used to represent an attribute id or a 

 id. The initial digit may not be zero. The smallest number of digits is six, and the maximum is 18.

ws = *( SP 

HTAB

 CR

LF )

Optional whitespace characters (space, tab, carriage return and linefeed) are ignored everywhere in the 

 except:

1. Whitespace within a conceptId is an error.
   
   Note: Whitespace before or after the last digit of a valid 

1.  is ignored.
   
2. Non-consecutive spaces within a term are treated as a significant character of the term.
   
   Note: Whitespace before the first or after the last non-whitespace character of a  term is ignored
   
3. Whitespace within the quotation marks of a concrete value is treated as a significant character.

SP = %x20

Space character.

HTAB = %x09

Tab character.

CR = %x0D

Carriage return character.

LF = %x0A

Line feed character.

QM = %x22 ; quotation mark

Quotation mark character.

BS = %x5C

Back slash character.

digit = %x30-39

Any digit 0 through 9.

zero = %x30

The digit 0.

digitNonZero = %x31-39

Digits 1 through 9, but excluding 0. The first character of a 

 is constrained to a digit other than zero.

nonwsNonPipe= %x21-7B / %x7D-7E / UTF8-2 / UTF8-3 / UTF8-4

Non whitespace (and non pipe) includes printable ASCII characters (these are also valid UTF8 characters encoded as one octet) and also includes all UTF8 characters encoded as 2- 3- or 4-octet sequences. It excludes space (which is %x20) and the pipe character "

" (which is %x7C), and excludes CR, LF, HTAB and other ASCII control codes. See RFC 3629 (  UTF-8, a 

 format of 

 10646 authored by the Network Working Group).

anyNonEscapedChar = HTAB / CR / LF / %x20-21 / %x23-5B / %x5D-7E / UTF8-2 / UTF8-3 / UTF8-4

anyNonEscapedChar includes any printable ASCII characters which do not need to be preceded by an escape character (i.e. "\"). This includes valid UTF8 characters encoded as one octet and all UTF8 characters encoded as 2, 3 or 4 octet sequences. It does, however, exclude the quotation mark (") and the backslash (). See RFC 3629 (  UTF-8, a 

 format of 

 10646 authored by the Network Working Group).

escapedChar = BS QM / BS BS

The double quotation mark and the back slash character must both be escaped within a string-based concrete value by preceding them with a back slash.

UTF8-2 = %xC2-DF UTF8-tail

UTF8 characters encoded as 2-octet sequences.

UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2(UTF8-tail) / %xED %x80-9F UTF8-tail /
%xEE-EF 2(UTF8-tail)

UTF8 characters encoded as 3-octet sequences.

UTF8-4 = %xF0 %x90-BF 2(UTF8-tail) / %xF1-F3 3(UTF8-tail) / %xF4 %x80-8F 2(UTF8-tail)

UTF8 characters encoded as 4-octet sequences.

UTF8-tail = %x80-BF

UTF8 characters encoded as 8-octet sequences.