Software Engineering for Students A Programming Approach

338 Chapter 27 ■ The unified process
Meeting the user’s needs requires no explanation. The second aim of the UP recognizes
that there are always risks associated with a development. Examples are changes
in user requirements and deadline overruns for components of the software. These can
seriously disrupt a project or even cause it to be abandoned.
To meet its aims, the UP makes use of a number of techniques including use cases,
iteration and emphasis on the architecture of the software.
A use case describes (in natural language) a small self-contained function that the system
provides for the user. A collection of use cases specify the requirements for a system.
(Use cases were discussed in Chapter 4 on requirements engineering.)
The UP mechanism for coping with risk is to proceed iteratively. This means that an
initial plan is constructed. Then some small amount of development is carried out.
Next, the outcome is assessed. In the light of the evaluation, a new plan is devised (or,
in the worst case, the project is abandoned).
The UP also emphasizes getting the architecture of the software right. By architecture
is meant the grand-scale structure of the software. For example, in a web-based
solution, what components run on the server and what components run on the client?
What type of database is to be used?
In summary the method makes heavy use of:
■ use cases
■ iteration
■ software architecture.
The UP consists of four phases: inception, elaboration, construction and transition.
We will now explore what they involve.
27.3 ● Phases of the UP
The UP consists of four phases: inception, elaboration, construction and transition, as
shown in Figure 27.1. We shall see later that within each phase are a number of iterations.
The four phases are, in outline:
Phase 1, inception
This consists of a feasibility study to establish whether the proposed system is worthwhile.
(We discussed how to carry out feasibility studies in Chapter 3.) An outline of the
major requirements is established. A decision is made to commit to the project, or not.
Phase 2, elaboration
During this phase:
■ the list of requirements is completed
■ the general architecture of the system is devised