Software Architect's Handbook

Top-down approach

A top-down approach starts with the entire system at the highest level, and then a process of decomposition begins to work downward toward more detail. The starting point is the highest level of abstraction. As decomposition progresses, the design becomes more detailed, until the component level is reached.

While the detailed design and implementation details of the components are not part of the architecture design, the public interfaces of the components are part of the design. It is the public interfaces that allow us to reason about how components will interact with each other.

A design using the top-down approach is typically performed iteratively, with increasing levels of decomposition. It is particularly effective ...