The second problem [with using UML for the purposes of this book] is that the Unified Modeling Language concentrates on implementation modeling rathe… - Martin Fowler

Refactoring is a disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior. Its heart is a series of small behavior preserving transformations. Each transformation (called a 'refactoring') does little, but a sequence of transformations can produce a significant restructuring. Since each refactoring is small, it's less likely to go wrong. The system is also kept fully working after each small refactoring, reducing the chances that a system can get seriously broken during the restructuring.

Transparency is valuable, but while many things can be made transparent in distributed objects, performance isn't usually one of them.

Often you'll see the same three or four data items together in lots of places: fields in a couple of classes, parameters in many method signatures. Bunches of data that hang around together really ought to be made into their own objects.