[SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] final action state      activity diagrams  final states, state diagrams  2nd  flow transitions  four-layer metamodeling archtecture  fragmentation period of development  functional requirements, use cases