In an amazingly short time, software has become critical to almost every aspect of modern life. From bank vaults to city stoplights, from telephone networks to DVD players, from automobile air bags to air traffic control systems, the world around us is regulated by code. Yet much software simply doesn"t work reliably: ask anyone who has watched a computer screen flush blue, wiping out hours of effort. All too often, software engineers say, code is bloated, ugly, inefficient and poorly designed; even when programs do function correctly, users find them too hard to understand. Groaning beneath the weight of bricklike manuals, bookstore shelves across the nation testify to the perduring dysfunctionality of software