Software Engineering for Students A Programming Approach

Tested
component
Figure 24.1 Top-down implementation
Tested
component
Tested
component
Stub
Component
Stub Stub
under test
24.5 ● Bottom-up implementation
24.5 Bottom-up implementation 317
This type of implementation starts with an architectural design for the software.
Bottom-up implementation starts with the lowest-level components of the system.
These are the components that everything else depends on, but that don’t use anything
themselves. In an OOD design these are the shared, reusable classes that form a common
library for the application to use. In many systems this is the software that accesses
the database.
The bottom-up implementation starts with the lowest-level components of the system.
These are the components that everything else uses, but that don’t use anything
themselves. The first task is to construct a test bed for each component. Figure 24.2
shows two components at the lowest level of a system and their test beds.
When the lowest level components have been tested in this manner, components are
combined into subsystems that are tested in a similar manner, again using a test bed
(Figure 24.3). The procedure continues until the complete system is finally assembled
and tested as a whole.
Bottom-up implementation suffers from the following drawbacks:
■ drivers are required during almost all the development
Test bed 1 Test bed 2
Component 1
under test
Component 2
under test
Figure 24.2 Bottom-up testing of the lowest-level components