• Continuing Change 
• Increasing Complexity
• Large program evolution
• Organizational stability
• Conservation of familiarity
• Continuing growth
• Declining quality
• Feedback system

• Maintenance to repair software faults
• Maintenance to adapt the software to a dfferent operating environment
• Maintenance to add to or modify the system's functionality

• Team stability
• Contractual responsibility
• Staff skills
• Program age and structure

• Whether a system change should be accepted depends, on the maintainability of the system components affected by that change
• Implementing system changes tends to degrade the system structure and hence reduce its maintainability
• Maintenance costs depend on the number of changes, and the costs of change implementation depend on the maintainability of system components

Examples of process metrics that can be used for assessing maintainability

• Number of requests for corrective maintainence
• Average time required for impact analysis
• Average time taken to implement a change request
• Number of outstanding change requests

• Change requests
• Impact analysis
• Release planning
• Fault repair
• Platform adaptation
• System enhancement
• Change implementation
• System release

• If a serious system fault occurs that has to be repaires to allow normal operation to continue
• If changes to the sysm's operating environment have unexpected effects that disrupt normal operation
• If there are anticipated changes to the businss running the system, such as the emergence of new compeitiors or the introduction of new legislation.

• Reduced risk
• Reduced cost

• Source code translation
• Reverse engineering
• Program structure improvement
• Program modularization
• Data re-engineering

• The quality of the software to be re-engineered
• The tool support available for re-engineering
• The extent of data conversion required
• The availability of expert sstaff

• Scrap the system completely
• Leave the system unchanged and continue with regular maintenance
• Re-engineer the system to improve its maintainability
• Replace all or part of the system with a new system

• Low quality, low business
• Low quality, high business value
• High quality, low business value
• High quality, high business value

• The use of the system
• The business processes that are supported
• The system dependability
• The system outputs

• Supplier stability
• Failure rate
• Age
• Performance
• Support requirements
• Maintenance costs
• Interoperability

• Understandability
• Documentation
• Data
• Performance
• Programming language
• Configuration management
• Test data
• Personnel skills

• The number of system change requests
• The number of user interfaces
• The volume of data used by the system