Importance of evolution

• Organizations have huge investments in their software systems – they are critical business assets.
• To maintain the value of these assets to the business, they must be changed and updated.
• The majority of the software budget in large companies is devoted to evolving existing software rather than developing new software.

Maintenance is inevitable

• The system requirements are likely to change while the system is being developed because the environment is changing. Therefore a delivered system won’t meet its requirements!
• Systems are tightly coupled with their environment. When a system is installed in an
  environment it changes that environment and therefore changes the system requirements.
• Systems MUST be maintained therefore if they are to remain useful in an environment.

Types of maintenance

• Maintenance to repair software faults
  • Changing a system to correct deficiencies in the way meets its requirements.
• Maintenance to adapt software to a different operating environment
  • Changing a system so that it operates in a different environment (computer, OS, etc.) from its initial implementation.
• Maintenance to add to or modify the system’s functionality
  • Modifying the system to satisfy new requirements.

Maintenance cost factors

• Team stability
  • Maintenance costs are reduced if the same staff are involved with them for some time.
• Contractual responsibility
• The developers of a system may have no contractual responsibility for maintenance so there is no incentive to design for future change.
• Staff skills
  • Maintenance staff are often inexperienced and have limited domain knowledge.
• Program age and structure
  • As programs age, their structure is degraded and they become harder to understand and change.

Evolution processes

• Evolution processes depend on
  • The type of software being maintained;
  • The development processes used;
  • The skills and experience of the people involved.
• Proposals for change are the driver for system evolution. Change identification and evolution continue throughout the system lifetime.

The system evolution process

Legacy system evolution

• Organizations that rely on legacy systems must choose a strategy for evolving these systems
  • Scrap the system completely and modify business processes so that it is no longer required;Continue maintaining the system;Transform the system by re-engineering to improve its maintainability;
  • Replace the system with a new system.
• The strategy chosen should depend on the system quality and its business value.

Legacy system categories

• Low quality, low business value
  • These systems should be scrapped.

• Low-quality, high-business value
  • These make an important business contribution but are expensive to maintain. Should be re-engineered or replaced if a suitable system is available.
• High-quality, low-business value
  • Replace with COTS, scrap completely or maintain.
• High-quality, high business value
  • Continue in operation using normal system maintenance.

Business value assessment

• Assessment should take different viewpoints into account
  • System end-users;
  • Business customers;
  • Line managers;
  • IT managers;
  • Senior managers.
• Interview different stakeholders and collate results.

System quality assessment

• Business process assessment
  • How well does the business process support the current goals of the business?
• Environment assessment
  • How effective is the system’s environment and how expensive is it to maintain?
• Application assessment
  • What is the quality of the application software system?

System measurement

• You may collect quantitative data to make an assessment of the quality of the application system
  • The number of system change requests;
  • The number of different user interfaces used by the system;
  • The volume of data used by the system.