Top-down versus bottom-up design approaches
There are two fundamental approaches to the design of software architecture. One is a top-down design approach, and the other is a bottom-up approach. These strategies apply to a variety of disciplines, including software architecture design. Let's look at both of them in more detail.
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...
