Software Engineering for Students A Programming Approach

304 Chapter 23 ■ Prototyping
a clear, concise understanding of their needs. The conventional specification is a narrative
description of a system that may be technical and time-consuming to read. The
larger the development team, including user representatives, the more difficult communication
becomes. Prototyping is one technique that attempts to address these problems
and provide possible solutions. The benefits of developing and demonstrating a
prototype early in the software process are:
■ misunderstandings between software developers and users may be identified
■ missing facilities may be revealed
■ difficult-to-use or confusing facilities may be identified and refined
■ software developers may find incomplete and/or inconsistent requirements.
There are sometimes other objectives:
■ to create an acceptable user interface
■ a working, albeit limited, system is available quickly to demonstrate the feasibility
and usefulness of the application to management
■ user training – a prototype system can be used for training users before the final system
has been delivered
■ to establish that some new technology will provide the facilities needed (e.g. does
Java provide sufficient security for electronic transfer of funds?).
An example of using prototyping for user interface design is given in Chapter 5.
23.3 ● Throwaway or evolutionary?
There are two types of prototype:
1. throwaway – the various versions of the system are constructed and then thrown
away. (The final system is implemented in some different way.)
2. evolutionary – an initial implementation evolves towards the final version. (The
prototype becomes the final system.)
For example, a throwaway prototype might be written very quickly in Visual Basic
to demonstrate the essential functions that a system will carry out. But then the software
might be rewritten using careful and systematic development methods.
Alternatively, an evolutionary prototype might be implemented in C# to demonstrate
to the user the main features of the system. Having checked that the system does
what is required, new features and facilities are added to the prototype, gradually transforming
it into its complete form.
In throwaway prototyping, the priority is to understand requirements that are
unclear and therefore requirements that are straightforward may never need to be
prototyped. In evolutionary prototyping, the first priority is to incorporate wellunderstood
requirements into the prototype then to move on to those requirements
that are unclear.