1 PROPAGATE 2? TO 2.1 TERMINAL TerminalExpression 2.1 LABEL LabelExpression 2.1.1? MessageSources 2.1.1.1? Controls WHERE 1 MessageSources = 2? ENVIRONMENT Expression 3? MESSAGE Expression 4? EXCEPTION Expression 1 Controls = 2? FINALIZE 2.1 DEFAULT 2.1 NONE 2.1.1? DELETE 2.1.1.1 DEFAULT 2.1.1.1 NONE