Software Evolution
Chapter 9 Software evolution 1
Topics covered
• Evolution processes
– Change processes for software systems
• Program evolution dynamics
– Understanding software evolution
• Software maintenance
– Making changes to operational software systems
• Legacy system management
– Making decisions about software change
Chapter 9 Software evolution 2
Software change
• Software change is inevitable
– New requirements emerge when the software is used;
– The business environment changes;
– Errors must be repaired;
– New computers and equipment is added to the system;
– The performance or reliability of the system may have to be improved.
• A key problem for all organizations is implementing and
managing change to their existing software systems.
Chapter 9 Software evolution 3
Importance of evolution
• Organisations 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 changing and
evolving existing software rather than
developing new software.
Chapter 9 Software evolution 4
A spiral model of development and
evolution
Chapter 9 Software evolution 5
Evolution and servicing
Chapter 9 Software evolution 6
Evolution and servicing
• Evolution
– The stage in a software system’s life cycle where it is in
operational use and is evolving as new requirements are
proposed and implemented in the system.
• Servicing
– At this stage, the software remains useful but the only changes
made are those required to keep it operational i.e. bug fixes
and changes to reflect changes in the software’s environment.
No new functionality is added.
• Phase-out
– The software may still be used but no further changes are
made to it.
Chapter 9 Software evolution 7
Evolution processes
• Software 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.
– Should be linked with components that are affected by the
change, thus allowing the cost and impact of the change to
be estimated.
• Change identification and evolution continues
throughout the system lifetime.
Chapter 9 Software evolution 8
Change identification and
evolution processes
Chapter 9 Software evolution 9
The software evolution process
Chapter 9 Software evolution 10
Change implementation
Chapter 9 Software evolution 11
