Sommerville-Software-Engineering-10ed

7.3 ■ Implementation issues 213
System
Application systems
(COTS)
Abstraction
Architectural and
design patterns
Software reuse
Component
Component
frameworks
Figure 7.13 Software
reuse
Programming
language libraries
Object
2. Configuration management During the development process, many different
versions of each software component are created. If you don’t keep track of
these versions in a configuration management system, you are liable to include
the wrong versions of these components in your system.
3. Host-target development Production software does not usually execute on the
same computer as the software development environment. Rather, you develop
it on one computer (the host system) and execute it on a separate computer (the
target system). The host and target systems are sometimes of the same type, but
often they are completely different.
7.3.1 Reuse
From the 1960s to the 1990s, most new software was developed from scratch, by
writing all code in a high-level programming language. The only significant reuse or
software was the reuse of functions and objects in programming language libraries.
However, costs and schedule pressure meant that this approach became increasingly
unviable, especially for commercial and Internet-based systems. Consequently, an
approach to development based on the reuse of existing software is now the norm for
many types of system development. A reuse-based approach is now widely used for
web-based systems of all kinds, scientific software, and, increasingly, in embedded
systems engineering.
Software reuse is possible at a number of different levels, as shown in Figure 7.13:
1. The abstraction level At this level, you don’t reuse software directly but rather
use knowledge of successful abstractions in the design of your software. Design
patterns and architectural patterns (covered in Chapter 6) are ways of representing
abstract knowledge for reuse.