Requirement Engineering

3.1 Requirement Engineering

We recall from our previous discussion that software development is not simply coding –
it is a multi-activity process. The process of software construction encompasses and
includes answers to the following questions:

• What is the problem to be solved?
• What are the characteristics of the entity that is used to solve the problem?
• How will the entity be realized?
• How will the entity be constructed?
• What approach will be used to uncover errors that were made in the design and construction of the entity?
• How will the entity be supported over the long term when users of the entity request corrections, adaptations, and enhancements?

These questions force us to look at the software development process from different angles and require different tools and techniques to be adopted at different stages and phases of the software development life cycle. Hence we can divide the whole process in 4 distinct phases namely vision, definition, development, and maintenance. Each one of these stages has a different focus of activity. During the vision phases, the focus is on why do we want to have this system; during definition phase the focus shifts from why to what needs to be built to fulfill the previously outlined vision; during development the definition is realized into design and implementation of the system; and finally during maintenance all the changes and enhancements to keep the system up and running and adapt to the new environment and needs are carried out. Requirement engineering mainly deals with the definition phase of the system. Requirement engineering is the name of the process when the system services and  constraints are established. It is the starting point of the development process with the focus of activity on what and not how.

Software Requirements Definitions
Before talking about the requirement process in general and discussing different tools and techniques used for developing a good set of requirements, let us first look at a few definitions of software requirements. Jones defines software requirements as a statement of needs by a user that triggers the development of a program or system.

Alan Davis defines software requirements as a user need or necessary feature, function, or attribute of a system that can be sensed from a position external to that system. According to Ian Summerville, requirements are a specification of what should be implemented. They are descriptions of how the system should behave, or of a system property or attribute. They may be a constraint on the development process of the system.

IEEE defines software requirements as:

1. A condition or capability needed by user to solve a problem or achieve an objective.
2. A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed document.
3. A documented representation of a condition or capability as in 1 or 2.

As can be seen, these definitions slightly differ from one another but essentially say the same thing: a software requirement is a document that describes all the services provided by the system along with the constraints under which it must operate.

In the next we will see Importance of Requirement in Software Engineering.