anchor.diff:  
   aggregate   : 'aggregate' ;
   
  -//booleanExpression : 'booleanExpression' ;
  -
   //varID       : 'varId';
   
   //WS          : [ \t\n\t] -> skip ;
  
positive.code:     : componentRef
      | constant
      ;
  
  //datasetExpression
  //    : 'dsTest'
  //    ;
  
  EQ_OPERATOR : ( EQ | NE | LE | LT | GE | GT ) ;
  EQ : '='  ;
  
negative.code:     | booleanExpression op=(OR|XOR) booleanExpression       # BooleanAlgebra
      | booleanParam op=(ISNULL|ISNOTNULL)                    # BooleanPostfix
      | op=NOT booleanExpression                              # BooleanNot
      | BOOLEAN_CONSTANT                                      # BooleanConstant
      ;
  
  