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An expression constraint is either a refined expression constraint, a compound expression constraint, a simple expression constraint, or an expression constraint enclosed in brackets.

A simple expression constraint includes exactly one focus concept, optionally preceded by a constraint operator. Any memberOf function in the focusConcept is processed prior to the constraintOperator being processed (if present).

A refined expression constraint includes a simple expression constraint followed by a refinement.

A compound expression constraint contains two or more simple expression constraints joined by either a conjunction, disjunction or exclusion. When potential ambiguity in binary operator precedence may occur, round brackets must be used to clearly disambiguate the order in which these operator are applied. Brackets are not required in expression constraints in which all binary operators are conjunctions, or all binary operators are disjunctions. Please note that unary operators (i.e. constraint operators and member of functions) are always applied before binary operators (i.e. conjunction, disjunction and exclusion).

A conjunction expression constraint combines two or more expression constraints with a conjunction ("and") operator. More than one conjunction may be used without brackets. However any compound expression constraint (using a different binary operator) that appears within a conjunction expression constraint must be enclosed by brackets.

A disjunction expression constraint combines two or more expression constraints with a disjunction ("or") operator. More than one disjunction may be used without brackets. However any compound expression constraint (using a different binary operator) that appears within a disjunction expression constraint must be enclosed by brackets.

An exclusion expression constraint combines two expression constrains with an exclusion ("minus") operator. A single exclusion operator may be used without brackets. However when the operands of the exclusion expression constraint are compound, these compound expression constraints must be enclosed by brackets.

A subexpression constraint, which appears within a compound expression constraint, must either be a simple expression constraint, or an expression constraint enclosed in brackets.

A focus concept is a concept reference or wild card, which is optionally preceded by a member of function. A memberOf function should be used only when the conceptReference refers to a reference set concept, or a wild card is used.

The 'memberOf' function returns the set of referenced components in the reference set whose concept identifier follows. In the brief syntax, the memberOf function is represented using the "^" symbol. In the long syntax, the text "memberOf " (case insensitive and followed by at least one white space) is also allowed.

A conceptReference is represented by a ConceptIdoptionally followed by a  term enclosed by a pair of "|" characters. Whitespace before or after the ConceptIdis 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.

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.

The  term must be the  term from a   that is associated with the   identified by the preceding  . For example, the  term could be the preferred  , or the preferred   associated with a particular translation. The  term may include valid  UTF-8 characters except for the pipe "

A wild card represents any concept in the given substrate. In the brief syntax, a wildcard is represented using the "*" symbol. In the long syntax, the text "ANY" (case insensitive) is also allowed.

A constraint operator is either 'childOf', 'descendantOrSelfOf', 'descendantOf', 'parentOf', 'ancestorOrSelfOf', or 'ancestorOf'.

In the brief syntax, the descendantOf operator is represented using the symbol "<". In the long syntax, the text "descendantOf" (case insensitive and followed by at least one white space) is also allowed.

In the brief syntax, the descendantOrSelfOf operator is represented using the symbols "<<". In the long syntax, the text "descendantOrSelfOf" (case insensitive and followed by at least one white space) is also allowed.

In the brief syntax, the childOf operator is represented using the symbols "<!". In the long syntax, the text "childOf" (case insensitive and followed by at least one white space) is also allowed.

In the brief syntax, the ancestorOf operator is represented using the symbol ">". In the long syntax, the text "ancestorOf " (case insensitive and followed by at least one white space) is also allowed.

In the brief syntax, the ancestorOrSelfOf operator is represented using the symbols ">>". In the long syntax, the text "ancestorOrSelfOf" (case insensitive and followed by at least one white space) is also allowed.

In the brief syntax, the parentOf operator is represented using the symbols ">!". In the long syntax, the text "parentOf" (case insensitive and followed by at least one white space) is also allowed.

A conjunction is represented either by the word "and" (case insensitive and followed by at least one white space), or by a comma.

A disjunction is represented by the word "or" (case insensitive and followed by at least one white space).

The exclusion operator is represented by the word "minus" (case insensitive and followed by at least one white space).

A refinement contains all the grouped and ungrouped attributes that refine the set of clinical meanings satisfied by the expression constraint. Refinements may represent the conjunction or disjunction of two smaller refinements, and may optionally be placed in brackets. Where both conjunction and disjunction are used, brackets are mandatory to disambiguate the intended meaning.

A conjunction refinement set consists of one or more conjunction operators, each followed by a subRefinement.

A disjunction refinement set consists of one or more disjunction operators, each followed by a subRefinement.

A subRefinement is either an attribute set, an attribute group or a bracketed refinement.

An attribute set contains one or more  -value pairs separated by a conjunction or disjunction operator. An attribute set may optionally be placed in brackets.

A conjunction attribute set consists of one or more conjunction operators, each followed by a subAttributeSet.

A disjunction attribute set consists of one or more disjunction operators, each followed by a subAttributeSet.

A subAttributeSet is either an attribute or a bracketed attribute set.

An   contains a collection of attributes that operate together as part of the   of the containing  constraint. An attribute group may optionally be preceded by a cardinality. An attribute group cardinality indicates the minimum and maximum number of attribute groups that must satisfy the given attributeSet constraint for the expression constraint to be satisfied.

An  -value pair expressing a single   of the containing  constraint. Either the attribute value must satisfy (or not) the given expression constraint, the attribute value is compared with a given numeric value (integer or decimal) using a numeric comparison operator, or the attribute value must be equal to (or not equal to) the given string value. The attribute may optionally be preceded by a cardinality constraint, a reverse flag and/or an attribute operator.

The cardinality represents a constraint on the minimum and maximum number of times that the given attribute or attribute group may appear in a matching expression. The cardinality is enclosed in square brackets with the minimum cardinality appearing first, followed by a separator (two dots in the brief syntax), and then the maximum cardinality.

A value that represents the minimum number of times that an attribute or attribute group may appear. The minimum cardinality must always be less than or equal to the maximum cardinality.

In the brief syntax, the minimum and maximum cardinality are separated by two dots (i.e. ".."). In the long syntax, the text "to" (case insensitive with at least one white space before and after) is also allowed between the two cardinalities.

A value that represents the maximum number of times that an attribute or attribute group may appear. A maximum cardinality of 'many' indicates that there is no limit on the number of times the attribute may appear.

In the brief syntax, a cardinality of 'many' is represented using the symbol "*". In the long syntax, the text "many" (case insensitive, with no trailing space) is also allowed.

When a reverse flag is used on an attribute, the matching relationships are traversed in the reverse of the normal direction. This means that the target concept of each relationship must match the focus concept to which the attribute is applied, while the source concept of the relationship must match the attribute value. In the brief syntax, the reverse flag is represented using the character "R" (in uppercase). In the long syntax, the text "reverseOf " (case insensitive) is also allowed.

An attribute operator indicates that instead of just matching the named attribute with the given attribute value, any descendants of or any descendants or self of the named attribute may match the given attribute value.

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. If the attribute name is not known then a wild card may be used to represent any attribute concept in the given substrate.

An expression constraint value is either a simple expression constraint, or is a refined or compound expression constraint enclosed in brackets.

Attributes whose value is a concept may be compared to an expression constraint using either equals ("=") or not equals ("!="). In the long syntax "<>" and "not =" (case insensitive) are also valid ways to represent not equals.

Attributes whose value is numeric (i.e. integer or decimal) may be compared to a specific concrete value using a variety of comparison operators, including equals ("="), less than ("<"), less than or equals ("<="), greater than (">"), greater than or equals (">=") and not equals ("!="). In the long syntax "<>" and "not =" (case insensitive) are also valid ways to represent not equals.

Attributes whose value is numeric may be compared to an expression constraint using either equals ("=") or not equals ("!="). In the long syntax "<>" and "not =" (case insensitive) are also valid ways to represent not equals.

A numeric value is either an integer or a decimal preceded by a hash ("#").

A string value includes one or more of any printable ASCII characters enclosed in quotation marks. Quotes and backslash characters within the string must be preceded by the escape character ("\").

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.

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

A non-negative integer value (i.e. positive integers or zero), without a preceding plus sign ("+").

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.

Optional whitespace characters (space, tab, carriage return, linefeed or a comment) 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   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.

Mandatory whitespace (i.e. space, tab, carriage return, linefeed or a comment) is required after certain keywords, including "And" and "Or".

A comment, which provides additional human-readable details about the expression constraint. Comments begin with a forward slash directly followed by a star (i.e. "/") and end with a star directly followed by a forward slash (i.e. "/").

A character that is not a star (i.e. not %x2A).

A star (i.e. "*") followed by a character that is not a forward slash (i.e. not "/").

A character that is not a forward slash (i.e. not "/").

Space character.

Tab character.

Carriage return character.

Line feed character.

Quotation mark character.

Any digit 0 through 9.

The digit 0.

Digits 1 through 9, but excluding 0.

The first character of a   is constrained to a digit other than zero.

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 "

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).

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 characters encoded as 2-octet sequences.

UTF8 characters encoded as 3-octet sequences.

UTF8 characters encoded as 4-octet sequences.

UTF8 characters encoded as 8-octet sequences.