2.3 Software design

Introduction

Software design is a process of defining the architecture, components, interfaces, and other characteristics of a system or component and planning for a software solution. After the purpose and specifications of software is determined, software developers will design or employ designers to develop a plan for a solution.

A software design may be platform-independent or platform-specific, depending on the availability of the technology called for by the design.

Viewed as a process, software design is the software engineering life cycle activity in which software requirements are analyzed in order to produce a description of the software’s internal structure that will serve as the basis for its construction. More precisely, a software design (the result) must describe the software architecture and the interfaces between those components. It must also describe the components at a level of detail that enable their construction.

Software design plays an important role in developing software: it allows software engineers to produce various models that form a kind of blueprint of the solution to be implemented. We can analyze and evaluate these models to determine whether or not they will allow us to fulfill the various requirements. We can also examine and evaluate various alternative solutions and trade-offs. Finally, we can use the resulting models to plan the subsequent development activities, in addition to using them as input and the starting point of construction and testing.

In a standard listing of software life cycle processes such as IEEE/EIA 12207 Software Life Cycle Processes, software design consists of two activities that fit between software requirements analysis and software construction:

• Software architectural design (sometimes called top-level design): describing software’s top-level structure and organization and identifying the various components.
• Software detailed design: describing each component sufficiently to allow for its construction.

Concepts of software design

The concepts, notions, and terminology introduced here form an underlying basis for understanding the role and scope of software design.

General design concepts

Software is not the only field where design is involved. In the general sense, we can view design as a form of problem-solving. For example, the concept of a wicked problem–a problem with no definitive solution–is interesting in terms of understanding the limits of design. A number of other notions and concepts are also of interest in understanding design in its general sense: goals, constraints, alternatives, representations, and solutions.

Context of software design

To understand the role of software design, it is important to understand the context in which it fits, the software engineering life cycle. Thus, it is important to understand the major characteristics of software requirements analysis vs. software design vs. software construction vs. software testing.