A critical aspect of all engineering disciplines is the elaboration of multiple approaches, trade-off analyses among them, and the eventual adoption of one. After requirements are agreed upon, you must examine a variety of architectures and algorithms. You certainly do not want to use an architecture simply because it was used in the requirements specification. After all, that architecture was selected to optimize understandability of the system's external behavior. The architecture you want is the one that optimizes conformance with requirements.
For example, architectures are generally selected to optimize throughput, response time, modifiability, portability, interoperability, safety, or availability, while also satisfying the functional requirements. The best way to do this is to enumerate a variety of software architectures, analyze (or simulate) each with respect to the goals, and select the best alternative. Some design methods result in specific architectures; so one way to generate a variety of architectures is to use a variety of methods.
