In a previous post I commented about Fred Brooks’ great conference when he received the Turing Award. He named it “The Design of Design”. In that conference he spends a lot of time discussing life cycle models and explaining why the Waterfall model is wrong (“dead wrong” as he calls it). And he also presented what he thought was a better model: the co-evolutionary model, attributing it to Maher and Cross. In this model, from a Problem P1 you get a Solution S1. And from P1 and S1 you get a new problem, P2. And from P2 and S1 you get a new Solution, S2. This simple concept explains that the problem and the solution evolve in parallel. And it’s one of the good things that Agile Methods have adopted. If you use agile methods, your lifecycle model is not only iterative and incremental. It’s also co-evolutionary. Let me explain this better.