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The following ABNF definition specifies the syntax of SNOMED CT Compositional Grammar.

expression =  ws [definitionStatus ws] subExpression ws

subExpression = focusConcept [ws ":" ws refinement]

definitionStatus = equivalentTo / subtypeOf

equivalentTo = "==="

subtypeOf = "<<<"

focusConcept = conceptReference *(ws "+" ws conceptReference) 

conceptReference = conceptId [ws "|" ws  term ws "|"]

conceptId = sctId

term = nonwsNonPipe *( *SP nonwsNonPipe )

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

attributeGroup = "{" ws attributeSet ws "}"

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

attribute = attributeName ws "=" ws attributeValue

attributeName = conceptReference

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

expressionValue = conceptReference / "(" ws subExpression ws ")"

stringValue = 1*(anyNonEscapedChar / escapedChar)

numericValue = ["-"/"+"] (decimalValue / integerValue)

integerValue =  digitNonZero *digit / zero

decimalValue = integerValue "." 1*digit

sctId = digitNonZero 5*17( digit )

ws = *( SP / HTAB / CR / LF ) ; optional white space

SP = %x20 ; space

HTAB = %x09 ; tab

CR = %x0D ; carriage return

LF = %x0A ; line feed

QM = %x22 ; quotation mark

BS = %x5C ; back slash

digit = %x30-39

zero = %x30

digitNonZero = %x31-39

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

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

escapedChar = BS QM / BS BS

UTF8-2 = %xC2-DF UTF8-tail

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

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

UTF8-tail = %x80-BF