expression ::=
 [(] {boolean_expression
    | character_expression
    | date_expression
    | numeric_expression} 
 [)]

boolean_expression ::=
 [NOT] 
 {boolean_constant_name
 | boolean_function_call
 | boolean_literal
 | boolean_variable_name
 | other_boolean_form}
 [{AND | OR} [NOT] 
 {boolean_constant_name
 | boolean_function_call
 | boolean_literal
 | boolean_variable_name
 | other_boolean_form}] 
 [{AND | OR} [NOT] 
 {boolean_constant_name
 | boolean_function_call
 | boolean_literal
 | boolean_variable_name
 | other_boolean_form}]...