The design of large computer programs and the software systems they implement is a complex task. An old saw in programming goes, "Software is harder than hardware," and it means that new computer hardware is developed faster and more easily than new computer software. There is certainly a degree of truth to this statement, though computer architects are unlikely to be pleased by the seeming trivialization of their domain!

Program design is not a totally unique discipline, and cannot be practiced on a stand-alone basis. To give some idea of what program design is in relation to other aspects of program development, we may say that program design is to programming what building architecture is to masonry. A good architect can, if he chooses, take off his jacket and do a mason's job, but his comprehension has to be greater, encompassing more than the mason's point...