Quote:

it is easy to modify it for iterative and spiral development models



Reading your answer and looking at your scheme again, I ask you: Is it easy, actually? At least, not in 2D...

A sort of 3D scheme comes to my my mind, on the lowest level a cycle of small boxes(lists and documents), above that a cycle of bigger boxes with parts of the smaller boxes in it etc.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt