Bill Venners: In your paper, "Is Design Dead?", you talk about planned design. What is planned design?
Martin Fowler: I distinguish between planned and evolutionary design. Planned design says that when you think about a piece of software, you create the design first, then you code it. A planned design could take the form of UML diagrams. Or you could express it in terms of dividing a system into subsystems and defining the interfaces between those subsystems. With planned design, there's a definite switch between the two modes of creating the design and then coding it. And those tasks may often be performed by different people. Architects come up with design. The developer then code it. The design is not necessarily considered completely fixed, but it is considered mostly fixed. You can argue that the better the design, the less it will change as you code it.
With evolutionary design, you expect the design to evolve slowly over the course of the programming exercise. There's no design at the beginning. You begin by coding a small amount of functionality, adding more functionality, and letting the design shift and shape.
The point I make in "Is Design Dead?" is that most people have encountered evolutionary design in an unconstrained and ill-disciplined environment and it doesn't work. You end up with a crappy design. And that's one reason why people gravitate towards planned design.
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