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The formal syntax for SNOMED CT expression templates (v1.1) is shown below. This syntax is derived by combining:

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; Compositional Grammar v2.4 with slot references (in blue)

expressionTemplate =  ws [ (definitionStatus / tokenReplacementSlot) ws] subExpression ws

subExpression = focusConcept [ws ":" ws refinement]

definitionStatus = equivalentTo / subtypeOf

equivalentTo = "===" 

subtypeOf = "<<<"

focusConcept = [templateInformationSlot ws] conceptReference *(ws "+" ws [templateInformationSlot ws] conceptReference) 

conceptReference = conceptReplacementSlot / expressionReplacementSlot / ( conceptId [ws "|" ws  term ws "|"] )

conceptId = sctId

term = nonwsNonPipe *( *SP nonwsNonPipe )

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

attributeGroup =   [ templateInformationSlot ws ] "{" ws attributeSet ws "}"

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

attribute = [ templateInformationSlot ws ] attributeName ws "=" ws attributeValue

attributeName = conceptReference

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

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

stringValue = 1*(anyNonEscapedChar / escapedChar)

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

integerValue =  digitNonZero *digit / zero

decimalValue = integerValue "." 1*digit

booleanValue = true / false

true = ("t"/"T") ("r"/"R") ("u"/"U") ("e"/"E")

false = ("f"/"F") ("a"/"A") ("l"/"L") ("s"/"S") ("e"/"E")

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

; Template Syntax v1.1

templateSlot =  templateReplacementSlot / templateInformationSlot

templateReplacementSlot = conceptReplacementSlot / expressionReplacementSlot / tokenReplacementSlot / concreteValueReplacementSlot

conceptReplacementSlot = "[[" ws  "+" ws  conceptReplacement [slotName ws] "]]"

expressionReplacementSlot = "[[" ws  "+" ws  expressionReplacement [slotName ws] "]]"

tokenReplacementSlot = "[[" ws  "+" ws  tokenReplacement [slotName ws] "]]"

concreteValueReplacementSlot = "[[" ws  "+" ws  concreteValueReplacement [slotName ws] "]]"

conceptReplacement = "id" ws [ "(" ws slotExpressionConstraint ws ")" ws]

expressionReplacement = ["scg" ws] ["(" ws slotExpressionConstraint ws ")" ws]

tokenReplacement = "tok" ws [ "(" ws slotTokenSet ws ")" ws]

concreteValueReplacement = stringReplacement / integerReplacement / decimalReplacement / booleanReplacement

stringReplacement = "str" ws [ "(" ws slotStringSet ws ")" ws]

integerReplacement   = "int" ws [ "(" ws slotIntegerSet ws ")" ws]

decimalReplacement = "dec" ws [ "(" ws slotDecimalSet ws ")" ws]

booleanReplacement = "bool" ws [ "(" ws slotBooleanSet ws ")" ws]

slotTokenSet = slotToken *(mws slotToken)

slotStringSet = slotString slotStringValue *(mws slotStringslotStringValue)

slotStringValue = QM stringValue QM

slotIntegerSet = ( slotIntegerValue / slotIntegerRange) *(mws (slotIntegerValue / slotIntegerRange))

slotDecimalSet = ( slotDecimalValue / slotDecimalRange) *(mws (slotDecimalValue / slotDecimalRange))

slotBooleanSet = slotBooleanValue *(mws slotBooleanValue)

slotBooleanValue = booleanValue

slotIntegerRange = ( slotIntegerMinimum to [ slotIntegerMaximum ] ) / ( to slotIntegerMaximum )

slotIntegerMinimum = [ exclusiveMinimum ] slotIntegerValue

slotIntegerMaximum = [ exclusiveMaximum ] slotIntegerValue

slotIntegerValue = "#" digitNonZero *digit " ["-"/"#+" zero] integerValue

slotDecimalRange = ( slotDecimalMinimum to [ slotDecimalMaximum ] ) / ( to slotDecimalMaximum )

slotDecimalMinimum = [ exclusiveMinimum ] slotDecimalValue

slotDecimalMaximum = [ exclusiveMaximum ] slotDecimalValue

slotDecimalValue = "#" integerValue "." 1*digit ["-"/"+"] decimalValue

exclusiveMinimum = ">"

exclusiveMaximum = "<"

slotBooleanValue = true / false

; true = ("t"/"T") ("r"/"R") ("u"/"U") ("e"/"E")

; false = ("f"/"F") ("a"/"A") ("l"/"L") ("s"/"S") ("e"/"E")

slotName = "@" (nonQuoteStringValue / slotStringslotStringValue)

slotToken = definitionStatus / memberOf / constraintOperator / conjunction / disjunction / exclusion / reverseFlag / expressionComparisonOperator / numericComparisonOperator / stringComparisonOperator / booleanComparisonOperator

slotString = QM slotStringValue QM

nonQuoteStringValue  = *(%x21 / %x23-26 / %x2A-3F / %x41-5A / %x5C / %x5E-7E)   ; string with no ws, quotes, at, square brackets or round brackets

templateInformationSlot  = "[[" ws slotInformation ws "]]"

slotInformation = [cardinality ws] [slotName ws] 

; Expression Constraint Language v1.4 - Note that some rules are commented out because they are repeated in the Compositional Grammar rules above.

slotExpressionConstraint = ws ( slotRefinedExpressionConstraint / slotCompoundExpressionConstraint / slotDottedExpressionConstraint / slotSubExpressionConstraint ) ws

slotRefinedExpressionConstraint = slotSubExpressionConstraint ws ":" ws slotEclRefinement

slotCompoundExpressionConstraint = slotConjunctionExpressionConstraint / slotDisjunctionExpressionConstraint / slotExclusionExpressionConstraint

slotConjunctionExpressionConstraint = slotSubExpressionConstraint 1*(ws conjunction ws slotSubExpressionConstraint)

slotDisjunctionExpressionConstraint = slotSubExpressionConstraint 1*(ws disjunction ws slotSubExpressionConstraint)

slotExclusionExpressionConstraint = slotSubExpressionConstraint ws exclusion ws slotSubExpressionConstraint

slotDottedExpressionConstraint = slotSubExpressionConstraint 1*(ws slotDottedExpressionAttribute)

slotDottedExpressionAttribute = dot ws slotEclAttributeName

slotSubExpressionConstraint = [constraintOperator ws] [memberOf ws] (slotEclFocusConcept / "(" ws slotExpressionConstraint ws ")")

slotEclFocusConcept = slotEclConceptReference / wildCard

dot = "."

memberOf = "^"

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

; conceptId = sctId

; term = 1*nonwsNonPipe *( 1*SP 1*nonwsNonPipe )

wildcard = "*"

constraintOperator = childOf / descendantOrSelfOf / descendantOf / parentOf / ancestorOrSelfOf / ancestorOf

descendantOf = "<"

descendantOrSelfOf = "<<"

childOf = "<!"

ancestorOf = ">"

ancestorOrSelfOf = ">>"

parentOf = ">!"

conjunction = (("a"/"A") ("n"/"N") ("d"/"D") mws) / ","

disjunction = ("o"/"O") ("r"/"R") mws

exclusion = ("m"/"M") ("i"/"I") ("n"/"N") ("u"/"U") ("s"/"S") mws

slotEclRefinement = slotSubRefinement ws [slotConjunctionRefinementSet / slotDisjunctionRefinementSet]

slotConjunctionRefinementSet = 1*(ws conjunction ws slotSubRefinement)

slotDisjunctionRefinementSet = 1*(ws disjunction ws slotSubRefinement)

slotSubRefinement = slotEclAttributeSet / slotEclAttributeGroup / "(" ws slotEclRefinement ws ")"

slotEclAttributeSet = slotSubAttributeSet ws [slotConjunctionAttributeSet / slotDisjunctionAttributeSet]

slotConjunctionAttributeSet = 1*(ws conjunction ws slotSubAttributeSet)

slotDisjunctionAttributeSet = 1*(ws disjunction ws slotSubAttributeSet)

slotSubAttributeSet = slotEclAttribute / "(" ws slotEclAttributeSet ws ")"

slotEclAttributeGroup = ["[" cardinality "]" ws] "{" ws slotEclAttributeSet ws "}"

slotEclAttribute = ["[" cardinality "]" ws] [reverseFlag ws] slotEclAttributeName ws (expressionComparisonOperator ws slotSubExpressionConstraint / numericComparisonOperator ws slotNumericValue / stringComparisonOperator ws slotStringValue / booleanComparisonOperator ws booleanValue)

cardinality = minValue to maxValue

minValue = nonNegativeIntegerValue

to = ".."

maxValue = nonNegativeIntegerValue / many

many = "*"

reverseFlag = "R"

slotEclAttributeName = slotSubExpressionConstraint

expressionComparisonOperator = "=" / "!="

numericComparisonOperator = "=" / "!=" / "<=" / "<" / ">=" / ">"

stringComparisonOperator = "=" / "!="

booleanComparisonOperator = "=" / "!="

slotNumericValue  = "#" numericValue

; stringValue = 1*(anyNonEscapedChar / escapedChar)

; numericValue = ["-"/"+"] (slotDecimalValue / slotIntegerValue)slotStringValue = QM 1*(anyNonEscapedChar / escapedChar) QMdecimalValue / integerValue)

; integerValue = digitNonZero *digit / zero

; decimalValue = integerValue "." 1*digit

; booleanValue = true / false

; true = ("t"/"T") ("r"/"R") ("u"/"U") ("e"/"E")

; false = ("f"/"F") ("a"/"A") ("l"/"L") ("s"/"S") ("e"/"E")

nonNegativeIntegerValue = (digitNonZero *digit ) / zero

; sctId = digitNonZero 5*17( digit )

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

mws = 1*( SP / HTAB / CR / LF / comment ) ; mandatory white space

comment = "/*" *(nonStarChar / starWithNonFSlash) "*/"

nonStarChar = SP / HTAB / CR / LF / %x21-29 / %x2B-7E /UTF8-2 / UTF8-3 / UTF8-4

starWithNonFSlash = %x2A nonFSlash

nonFSlash = SP / HTAB / CR / LF / %x21-2E / %x30-7E /UTF8-2 / UTF8-3 / UTF8-4

; 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 = SP / 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

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