Page 11 - DCAP405_SOFTWARE_ENGINEERING

Software Engineering

Notes
Figure 1.1: Failure Curve for Hardware

Burn in Useful Life Wear out

Failure Rate

Time
Because the software does not undergo environmental degradation, its failure curve ideally
should flatten out after the initial stage of its life. The initial failure rate is high because of
undiscovered defects. Once these defects are fixed, the curve flattens at a later stage. Thus, the
software does not wear out but deteriorates.
The actual curve as shown in Figure 1.2 can explain the contradiction stated above. Because
software undergoes changes during its lifetime as a part of the maintenance activities, new
defects creep in causing the failure rate to rise (spike). While the software enters its steady state
further more changes are added which induce further more defects and hence, spikes in the
failure rate.
Figure 1.2: Failure Curve for Software

Test/Debug Useful Life Obsolescence

Failure Rate Upgrade Upgrade Upgrade

Time

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