Module SEO01 Software Evolution

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Module SE-O-01Software Evolution
Topic 2 Evolution within development life cycles
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Contents

• Traditional vs evolutionary process model
• Examples of evolutionary models

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Traditional process model

• E.g., waterfall process model (Royce, 1970)
• inspired by established engineering disciplines
• maintenance final phase only bug fixing and
  minor adjustments

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Evolutionary process model

• Reflects reality better

version 1.
0
version 2.
0
Require ment
Require ment
s
s
Design
Design
Implemen tation
Implemen tation
evolution
evolution
Testing
Testing
Deploy ment
Deploy ment
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Evolution processes

• Main characteristics
• change requests are the driver for software
  evolution
• change identification and evolution continue
  throughout the software lifetime
• The choice of a particular evolution process
  depends on
• The type of software being maintained
• The development processes used
• The skills and experience of the people involved

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Evolution processes

• Change identification and evolution
• (taken from Sommerville)

Change identification process
New System
Change proposals
Software evolution process
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Contents

• Traditional vs evolutionary process model
• Examples of evolutionary models

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Evolutionary process model

• Any iterative, incremental process model can be
  used for the software evolution process
• Spiral Model
• Extreme Programming
• Reuse-oriented development
• Staged life-cycle
• Change mini cycle

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Evolutionary process model Example 1

• Concurrent development model
• (taken from Sommerville)

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Evolutionary process model Example 2

• Spiral model of evolution

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Evolutionary process model Example 3

• Staged life-cycle model Bennet Rajlich 1999

Initial development

evolution changes
evolutio
n
(preserves architectural integrity
evolutio
n
evolution
versio
n
2
Version 3
servicing patches
servicin
g
servicin
g
servicing
versio
n
2
Version 3
pha
e-ou
t
pha
s
t
phase-out
versio
n
2
Version 3
close-dow
n
close-dow
n
close-down
versio
n
2
Version 3
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Evolutionary process model Example 4

• Change mini-cycle Yau 1978
• Request for change
• Planning phase
• Program comprehension
• Change impact analysis
• Change implementation
• Restructuring/refactoring for change
• Change propagation
• Verification and validation
• Re-documentation
• to avoid software erosion

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Evolutionary process model Example 4

• Sommerville's software evolution process

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Evolutionary process model Urgent change requests

• Urgent changes
• may have to be implemented without going through
  all stages of the software engineering process
• They are needed when
• a serious system fault has to be repaired
• changes to the systems environment (e.g. an OS
  upgrade) have unexpected effects
• business changes require a very rapid response
  (e.g. the release of a competing product)