Overview

The design activity begins when the requirements document for the software to be developed is available and the architecture has been designed. During design we further refine the architecture. Generally, design focuses on the what we have called the module view in Chapter 4. That is, during design we determine what modules should the system have and which have to be developed. Sometimes, the module view may effectively be a module structure of each component in the architecture. That is, the design exercise determines the module structure of the components. However, this simple mapping of components and modules may not always hold. In that case we have to ensure that the module view created in design is consistent with the architecture.

The design of a system is essentially a blueprint or a plan for a solution for the system. Here we consider a system to be a set of modules with clearly defined behavior which interact with each other in a defined manner to produce some behavior or services for its environment. A module of a system can be considered a system, with its own modules.

The design process for software systems often has two levels. At the first level the focus is on deciding which modules are needed for the system, the specifications of these modules, and how the modules should be interconnected. This is what is called the system design or top-level design. In the second level, the internal design of the modules, or...