Zigzag Pattern

The zigzag pattern describes the relationship between the problem space and the solution space, or, in other words, between the requirements and the product architecture.

Requirements should not anticipate the solution. They describe the What, and the product architecture describes the How. It sounds easy, but it is not easy.

Requirements are solution-free, and they contain solution aspects at the same time. It depends on the viewpoint and level of abstraction.

Let's assume that you have solution-free requirements (I argue that these requirements are not viable in practice). Now, you derive a product architecture that satisfies the requirements and you get the typical what/how pair. For example, you have requirements for a transportation system for people, and you derive a product architecture that specifies a car. The car solution leads to new requirements that contain aspects of that solution, for example, requirements about the engine of the car and self-driving capabilities...