Software change - ESSeRE

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Program evolution dynamics ● ● ● Program evolution dynamics is the study of the processes of system change. After major empirical studies, Lehman and Belady (1985) proposed that there were a number of ‘laws’ which applied to all systems as they evolved. There are sensible observations rather than laws. They are applicable to large systems developed by large organisations. Perhaps less applicable in other cases. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 21 Slide 8
Lehman’s laws Law Continuing change Increasing complexity Large program evolution Organisational stability Conservation of familiarity Continuing growth Declining quality Description A program that is used in a real-world environment necessarily must change or become progressively less useful in that environment. As an evolving program changes, its structure tends to become more complex. Extra resources must be devoted to preserving and simplifying the structure. Program evolution is a self-regulating process. System attributes such as size, time between releases and the number of reported errors is approximately invariant for each system release. Over a programÕs lifetime, its rate of development is approximately constant and independent of the resources devoted to system development. Over the lifetime of a system, the incremental change in each release is approximately constant. The functionality offered by systems has to continually increase to maintain user satisfaction. The quality of systems will appear to be declining unless they are adapted to changes in their operational environment. Feedback system Evolution processes incorporate multi-agent, multi-loop feedback systems and you have to treat them as feedback systems to achieve significant product improvement. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 21 Slide 9
Page 1 and 2: Software evolution: Software Change
Page 3 and 4: Topics covered ● ● Strategies f
Page 5 and 6: Software change strategies ● ●
Page 7: Spiral model of evolution Specifica
Page 11 and 12: Software maintenance ● ● ● Mo
Page 13 and 14: Types of maintenance ● ● ● Ma
Page 15 and 16: Distribution of maintenance effort
Page 17 and 18: Maintenance costs ● Cost-effectiv
Page 19 and 20: Maintenance cost factors ● ●
Page 21 and 22: Maintenance prediction ● Maintena
Page 23 and 24: Change prediction ● ● ● Predi
Page 25 and 26: Process metrics ● ● Process mea
Page 27 and 28: Change identification and evolution
Page 29 and 30: Change implementation Proposed chan
Page 31 and 32: Urgent change ● ● ● It’s us
Page 33 and 34: Architectural evolution ● ● The
Page 35 and 36: Legacy systems distribution D e s k
Page 37 and 38: User Interface Distribution ● ●
Page 39 and 40: Key points ● Software change stra
Page 41 and 42: System re-engineering ● ● ● R
Page 43 and 44: Forward and re-engineering S ystem
Page 45 and 46: Reengineering process activities
Page 47 and 48: Reengineering cost factors ● ●
Page 49 and 50: System quality and business value H
Page 51 and 52: Business value assessment ● ● A
Page 53 and 54: Business process assessment ● ●
Page 55 and 56: Environment assessment 2 ©Ian Somm
Page 57 and 58: Application assessment 2 Programmin
Page 59 and 60:
Key points ● ● ● ● Software
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Software change - ESSeRE

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