Software Engineering for Students A Programming Approach

Therefore, in summary:
■ the product of a throwaway prototype is a specification
■ the product of an evolutionary prototype is a system.
23.4 ● Throwaway prototyping
23.4 Throwaway prototyping 305
The starting point for throwaway prototyping is an outline specification for the software.
A throwaway prototype implements only those requirements that are poorly
understood. It is discarded after the desired information is learned. After the prototype
is complete, the developer writes a full specification, incorporating what was learned,
and then constructs a full-scale system based on that specification. Thus the purpose of
throwaway prototyping is the formulation of a validated specification.
Throwaway prototyping is sometimes called rapid prototyping and as the name
suggests, a rapid prototype should cost very little and take very little time to develop.
The emphasis is on using whatever methods are available to produce a system that can
be demonstrated to the user. Typically the only noticeable difference between the
prototype and the desired system is its performance, or in the volumes of data that it
handles. Rapid prototyping seems to contradict the idea of using systematic, careful
methods during development; a prototype is produced in as quick (and perhaps as
dirty) a manner as possible.
To be effective, throwaway prototyping is carried out within a systematic framework.
An overview of throwaway prototype development is shown in Figure 23.1.
The stages of throwaway prototyping are:
1. draw up an outline specification – the first step in throwaway prototyping is the
creation of an initial, often partial, specification. This specification contains areas
of uncertainty.
2. establish objectives – what is the prototype to be used for? What aspects of the proposed
system should it reflect? What can be learned from the prototype? The
objective may be to develop a system to prototype the user interface, to validate
functional requirements, to explore uncertain new technologies or to demonstrate
the feasibility of the application to management. The same prototype cannot meet
all objectives. The areas that are most often prototyped are the user interface, and
uncertain or vague functions.
3. select functions – the next stage is to decide what to put into and what to leave out
of the prototype. This is determined by the objectives of the system. If the purpose
of prototyping is to clarify users’ requirements, then the uncertain areas are the
candidates for prototyping. The development of a working model allows the developers
to make sure that the solution they are proposing will satisfy the requirements
and perform effectively. Depending on the objectives, it may be decided to
prototype all system functions but at reduced level. Alternatively a subset of system
functions may be included in the prototype.