Sommerville-Software-Engineering-10ed

9.3 ■ Software maintenance 275
What parts of the system are
most likely to be affected by
change requests?
Predicting
maintainability
What parts of the system
will be the most expensive
to maintain?
Predicting system
changes
Predicting
maintenance
costs
What will be the lifetime
maintenance costs of this
system?
How many change
requests can be
expected?
What will be the costs of
maintaining this system
over the next year?
Figure 9.13
Maintenance prediction
2. The number of inherently volatile system requirements As I discussed in Chapter 4,
requirements that reflect organizational policies and procedures are likely to be
more volatile than requirements that are based on stable domain characteristics.
3. The business processes in which the system is used As business processes
evolve, they generate system change requests. As a system is integrated with
more and more business processes, there are increased demands for changes.
In early work on software maintenance, researchers looked at the relationships
between program complexity and maintainability (Banker et al. 1993; Coleman et al.
1994; Kozlov et al. 2008). These studies found that the more complex a system or
component, the more expensive it is to maintain. Complexity measurements are particularly
useful in identifying program components that are likely to be expensive to
maintain. Therefore, to reduce maintenance costs you should try to replace complex
system components with simpler alternatives.
After a system has been put into service, you may be able to use process data to
help predict maintainability. Examples of process metrics that can be used for assessing
maintainability are:
1. Number of requests for corrective maintenance An increase in the number of
bug and failure reports may indicate that more errors are being introduced into
the program than are being repaired during the maintenance process. This may
indicate a decline in maintainability.
2. Average time required for impact analysis This is related to the number of program
components that are affected by the change request. If the time required
for impact analysis increases, it implies that more and more components are
affected and maintainability is decreasing.