The following ABNF definition specifies the Brief Syntax of the SNOMED CT Expression Constraint Language.

expressionConstraint = ws ( refinedExpressionConstraint / compoundExpressionConstraint / dottedExpressionConstraint / subExpressionConstraint ) ws

refinedExpressionConstraint = subExpressionConstraint ws ":" ws eclRefinement

compoundExpressionConstraint = conjunctionExpressionConstraint / disjunctionExpressionConstraint / exclusionExpressionConstraint

conjunctionExpressionConstraint = subExpressionConstraint 1*(ws conjunction ws subExpressionConstraint)

disjunctionExpressionConstraint = subExpressionConstraint 1*(ws disjunction ws subExpressionConstraint)

exclusionExpressionConstraint = subExpressionConstraint ws exclusion ws subExpressionConstraint

dottedExpressionConstraint = subExpressionConstraint 1*(ws dottedExpressionAttribute)

dottedExpressionAttribute = dot ws eclAttributeName

subExpressionConstraint = [constraintOperator ws] [memberOf ws] (eclFocusConcept / "(" ws expressionConstraint ws ")") *(ws filterConstraint)

eclFocusConcept = eclConceptReference / wildCard

dot = "."

memberOf = "^"

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

eclConceptReferenceSet = "(" ws eclConceptReference *(mws eclConceptReference) ws ")"

conceptId = sctId

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

wildCard = "*"

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

descendantOf = "<"

descendantOrSelfOf = "<<"

childOf = "<!"

childOrSelfOf = "<<!"

ancestorOf = ">"

ancestorOrSelfOf = ">>"

parentOf = ">!"

parentOrSelfOf = ">>!"

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

eclRefinement = subRefinement ws [conjunctionRefinementSet / disjunctionRefinementSet]

conjunctionRefinementSet = 1*(ws conjunction ws subRefinement)

disjunctionRefinementSet = 1*(ws disjunction ws subRefinement)

subRefinement = eclAttributeSet / eclAttributeGroup / "(" ws eclRefinement ws ")"

eclAttributeSet = subAttributeSet ws [conjunctionAttributeSet / disjunctionAttributeSet]

conjunctionAttributeSet = 1*(ws conjunction ws subAttributeSet)

disjunctionAttributeSet = 1*(ws disjunction ws subAttributeSet)

subAttributeSet = eclAttribute / "(" ws eclAttributeSet ws ")"

eclAttributeGroup = ["[" cardinality "]" ws] "{" ws eclAttributeSet ws "}"

eclAttribute = ["[" cardinality "]" ws] [reverseFlag ws] eclAttributeName ws (expressionComparisonOperator ws subExpressionConstraint / numericComparisonOperator ws "#" numericValue / stringComparisonOperator ws QM stringValue QM / booleanComparisonOperator ws booleanValue)

cardinality = minValue to maxValue

minValue = nonNegativeIntegerValue

to = ".."

maxValue = nonNegativeIntegerValue / many

many = "*"

reverseFlag = "R"

eclAttributeName = subExpressionConstraint

expressionComparisonOperator = "=" / "!="

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

stringComparisonOperator = "=" / "!="

booleanComparisonOperator = "=" / "!="

filterConstraint = "{{" ws filter *(ws "," ws filter) ws "}}"

filter = termFilter / languageFilter / typeFilter / dialectFilter

termFilter = termKeyword ws booleanComparisonOperator ws (typedSearchTerm / typedSearchTermSet)

termKeyword = ("t"/"T") ("e"/"E") ("r"/"R") ("m"/"M")

typedSearchTerm = ( [ match ws ":" ws ] matchSearchTermSet ) / ( wild ws ":" ws wildSearchTermSet )

typedSearchTermSet = "(" ws typedSearchTerm *(mws typedSearchTerm) ws ")"

wild = ("w"/"W") ("i"/"I") ("l"/"L") ("d"/"D")

match = ("m"/"M") ("a"/"A") ("t"/"T") ("c"/"C") ("h"/"H")

matchSearchTerm = 1*(nonwsNonEscapedChar / escapedChar)

matchSearchTermSet = QM ws matchSearchTerm *(mws matchSearchTerm) ws QM

wildSearchTerm = 1*(anyNonEscapedChar / escapedWildChar)

wildSearchTermSet = QM wildSearchTerm QM

languageFilter = language ws booleanComparisonOperator ws (languageCode / languageCodeSet)

language = ("l"/"L") ("a"/"A") ("n"/"N") ("g"/"G") ("u"/"U") ("a"/"A") ("g"/"G") ("e"/"E")

languageCode = 2alpha

languageCodeSet = "(" ws languageCode *(mws languageCode) ws ")"

typeFilter = typeIdFilter / typeTokenFilter

typeIdFilter = typeId ws booleanComparisonOperator ws (eclConceptReference / eclConceptReferenceSet)

typeId = ("t"/"T") ("y"/"Y") ("p"/"P") ("e"/"E") ("i"/"I") ("d"/"D")

typeTokenFilter = type ws booleanComparisonOperator ws (typeToken / typeTokenSet)

type = ("t"/"T") ("y"/"Y") ("p"/"P") ("e"/"E")

typeToken = synonym / fullySpecifiedName / definition

typeTokenSet = "(" ws typeToken *(mws typeToken) ws ")"

synonym = ("s"/"S") ("y"/"Y") ("n"/"N")

fullySpecifiedName = ("f"/"F") ("s"/"S") ("n"/"N")

definition = ("d"/"D") ("e"/"E") ("f"/"F")

dialectFilter = (dialectIdFilter / dialectAliasFilter) [ ws acceptabilitySet ]

dialectIdFilter = dialectId ws booleanComparisonOperator ws (eclConceptReference / dialectIdSet)

dialectId = ("d"/"D") ("i"/"I") ("a"/"A") ("l"/"L") ("e"/"E") ("c"/"C") ("t"/"T") ("i"/"I") ("d"/"D")

dialectAliasFilter = dialect ws booleanComparisonOperator ws (dialectAlias / dialectAliasSet)

dialect = ("d"/"D") ("i"/"I") ("a"/"A") ("l"/"L") ("e"/"E") ("c"/"C") ("t"/"T")

dialectAlias = alpha *( dash / alpha / integerValue)

dialectAliasSet = "(" ws dialectAlias [ws acceptabilitySet] *(mws dialectAlias [ws acceptabilitySet] ) ws ")"

dialectIdSet"(" ws eclConceptReference [ws acceptabilitySet] *(mws eclConceptReference [ws acceptabilitySet] ) ws ")"

acceptabilitySet = acceptabilityIdSet / acceptabilityTokenSet

acceptabilityIdSet = eclConceptReferenceSet

acceptabilityTokenSet = "(" ws acceptabilityToken *(mws acceptabilityToken) ws ")"

acceptabilityToken = acceptable / preferred

acceptable = ("a"/"A") ("c"/"C") ("c"/"C") ("e"/"E") ("p"/"P") ("t"/"T")

preferred = ("p"/"P") ("r"/"R") ("e"/"E") ("f"/"F") ("e"/"E") ("r"/"R")

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

stringValue = 1*(anyNonEscapedChar / escapedChar)

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

star = %x2A  ; asterisk

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

escapedWildChar = BS QM / BS BS / BS star

nonwsNonEscapedChar = %x21 / %x23-5B / %x5D-7E / UTF8-2 / UTF8-3 / UTF8-4

alpha = %x41-5A / %x61-7A

dash = %x2D

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