Software Engineering for Students A Programming Approach

Reuse components
23.6 Rapid prototyping techniques 309
The time needed to develop a prototype can be reduced if many parts of the system can
be reused rather than designed and implemented. Prototypes can be constructed quickly
if there is a library of reusable components and some mechanism to combine the
components into systems. The reusable components may also be used in the final system,
thus reducing its development cost. An example of this approach to prototyping
is found in the Unix operating system (Chapter 18 on Scripting). The success of
Smalltalk as a prototyping language is as much due to its reusable component libraries
as to the inbuilt language facilities.
Use a stand-alone machine
It is often possible to construct a system that appears realistic, but is in fact massively
incomplete. For example, if a network solution is to be developed, a prototype running
on a stand-alone computer is created. This simulates the complete system for the purpose
of validation. But the developer is freed from considerations of networking, large
data volumes and possible performance problems that would need to be considered in
the production version of the system.
Ignore error handling
In many systems as much as one-half of the software is concerned with error handling.
This includes:
■ validation of user data input from keyboards
■ handling input-output device errors
■ exception handling software
■ fault tolerant software.
Omit features
It may be that some features can simply be omitted in a prototype. Examples are logging
software, security and authentication features. These components of a productionquality
system can be significantly costly in development effort and so their omission
makes construction of a prototype quicker.
Ignore functionality
This type of prototype is aimed simply at establishing an acceptable user interface. For
example, suppose we were setting out to develop a new word processor (Appendix A).
We could, very quickly, create a mock-up of what would appear on the screen, while the
actual functions of the word processor are simply not implemented. This type of prototype
is often used during the design of the user interface (see Chapter 5).