Introduction to (software) design

Finally, although a software design is correct, it may not be followed as such during its implementation. So, we must be aware that wrong implementation of a design can lead to wrong software just like a wrong design would.

We understand that software design can lead to some drawbacks that are not to be ignored, but its advantages, as we have seen, are very relevant too. Considering all this, we believe that understanding the fundamentals of (software) design, as well good practices, guidelines, and enabling techniques are essential to an aspiring architect.

Elements of software design process

The design process can be described as the process of choosing a representation of a solution from a set of alternatives, given the constraints towards a set of goals. It can be divided in two phases : diversification and convergence.

The diversification is the phase of generating alternatives. Not necessarily documents describing a possible solution, but, at least, on the designer's mind. These alternatives are the solution candidates and are generated/obtained from knowledge, catalogs, or previous experience. During the convergence phase, the designer chooses the alternative (or the combination of alternatives) that meets the intended goals. The alternative selected will be the solution, which will meet the constraints imposed by the problem domain. The solution then may be described using some representation. The representation chosen must fit its purpose: describe the solution and the process to build the artifact that reaches the intended goals.

From the paragraph above, we must emphasize the following elements: goals , constraints , alternatives , representations , and solutions . These elements together define a conceptual framework that helps to understand the software design process.

Goals

Design begins with a need. If something is to be designed, though to be built, it is because the outcome of the design process will fulfill this need. In Software Engineering, the necessity starts from a customer who specifies what are her needs and therefore what are the goals to be achieved with the software system to be designed. So, the goal of the design process is to achieve a solution that will solve the customer's needs . In software design, goals are also referred to as requirements. Software design is mainly concerned on two types of requirements: functional and nonfunctional requirements.

A functional requirement specifies the functionality that a system will exhibit. In other words, what the system is to perform according to the customer. For example, a functional requirement for a sorting program is to provide the ability to sort integers. Another example could be related to a software system that manages the inventory of a movie rental store. If we were to enumerate the functional requirements of a system like this, among them would be: the ability to search for a movie by its keywords, the ability to perform a movie rental, the ability to perform a movie return, and many others.