It is necessary to know when to stop modeling. The tendency with Object Oriented modeling is to keep going forever. The effort is discontinuous to the reward of doing so, and the result is often bloated, unusable code that resembles a fourth century Scholastic's swipe at biology. There are several cases in the Arlow / Neustadt Book that approach this insanity, and we'll do our best not to drive the project off the cliff by making it too taxonomical.