Information Technology Reference
In-Depth Information
Chapter 5
Requirements Elicitation
5.1 What are Requirements?
Requirements define expected services of the system and constraints that the system
must obey. These services can be grouped into those that describe the scope of the
system and those that comprise the business functions, which are called functional
requirements. Statements can be classified into different categories of restrictions
imposed on a system; these are called constraints (Maciaszek
2001
). Requirements
derived from the application domain of the system rather than from the specific
needs of users are called domain requirements. A requirement can be a description
of what a system must do. This type of requirement specifies something that the
delivered system must be able to do. Another type of requirement is one that
specifies something about the system itself, and how well it performs its functions.
Such requirements are often called 'non-functional requirements', 'performance
requirements' or 'quality of service requirements.'
5.1.1 Functional Requirements
Functional requirements are associated with specific functions, tasks, or behaviors
the system must fully support. The functional requirements address the quality
characteristic of functionality while the other quality characteristics are concerned
with various kinds of non-functional requirements. Use cases have quickly become
a widespread practice for capturing functional requirements. This is especially true
in the object-oriented community where they originated, however, their applica-
bility is not limited to object-oriented systems.
