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A A logical expression used to select datasets that meet specific criteria. Here's a loose grammar which defines expressions:
Expr ::= Expr
Expr ::= '(' Expr ')'
Expr ::= '!' Expr
Expr ::= Expr LogOp Expr
LogOp ::= '&&' | '||'
Expr ::= Comparable CmpOp Comparable
CmpOp ::= '==' | '!=' | '>=' | '<='
Comparable ::= "String" -- a String constant must be enclosed in double quotes
Comparable ::= Number
Comparable ::= Identifier
Comparable ::= UnOp Comparable
UnOp ::= '-' | '+'
Comparable ::= Comparable BinOp Comparable
BinOp ::= '/' | '*' | '+' | '-'