1. CS 577b Software Engineering II -- Introduction
19 April 2017
Software Maintenance based on Software Engineering Body of Knowledge (SWEBOK)
CS 577b Software Engineering II
Supannika Koolmanojwong
March 10, 2011
© USC Center for Software Engineering

2. Outline Software Maintenance Fundamentals
Key Issues in Software Maintenance
Maintenance Process
Techniques for Maintenance
03/02/2011
© 2011 USC-CSSE

3. Definition IEEE standard [IEEE 1219-98:s3.1.12]:
“the modification of a software product after delivery to correct faults, to improve performance or other attributes , or to adapt the product to a modified environment.”
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4. Nature of Maintenance
Sustain the software product throughout its operational life cycle
Modification requests are logged and tracked
Impact of the proposed changed is determined
Code and artifacts are modified
Testing is conducted
New version of software product is released
Need training and daily support
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6. Why we need a software maintenance ?
Correct faults
Improve the design
Implement enhancements
Interface with other systems
Adapt programs so that different hardware, software, system features, and telecommunications facilities can be used
Migrate legacy software
Retire software
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7. Maintainer’s activities
Maintaining control over the software's day-to-day functions
Maintaining control over software modification
Perfecting existing functions
Preventing software performance from degrading to unacceptable levels
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8. Cost of Software Maintenance
Common perception
software maintenance cost = fixes faults
80% - non-corrective actions
BUT, many managers put enhancement and correction together
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9. Factors influencing maintenance costs
Application type
Software novelty/uniqueness
Software maintenance staff availability
Software life span
Hardware characteristics
Quality of software design, construction, documentation and testing
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10. Software Maintenance Categories
Correction
Enhancement
Proactive
Preventive
Perfective
Reactive
Corrective
Adaptive
Corrective maintenance: Reactive modification of a software product performed after delivery to correct discovered problems
Adaptive maintenance: Modification of a software product performed after delivery to keep a software product usable in a changed or changing environment
Perfective maintenance: Modification of a software product after delivery to improve performance or maintainability
Preventive maintenance: Modification of a software product after delivery to detect and correct latent faults in the software product before they become effective faults
03/02/2011
© 2011 USC-CSSE

11. Outline Software Maintenance Fundamentals
Key Issues in Software Maintenance
Maintenance Process
Techniques for Maintenance
03/02/2011
© 2011 USC-CSSE

12. Key Issues in Software Maintenance
Technical issues
Management issues
Cost estimation
Measures
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13. 1) Technical Issues Limited understanding Testing
40% to 60% of the maintenance effort is devoted to understanding the software to be modified
Testing 
Full testing is costly
Regression testing - retesting of a software or component to verify that the modifications have not caused unintended effects
When to test (possible for offline testing?)
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14. 1) Technical Issues Impact analysis
analysis of the impact of a change in existing software
identify all systems and software products, estimate of the resources needed
Change request; modification request (MR); problem report (PR)
Objectives of Impact Analysis
Determine scope of change in order to plan and implement work
Develop estimates of resources needed to perform the work
Analyze cost/benefits of the requested change
Communicate to others of the complexity of a given change 
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15. 1) Technical Issues Maintainability
In order to save cost, determine maintainability during development process, review it and control it
Not emphasized during development process
Mature process helps enhancing maintainability
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16. 2. Management Issues Alignment with organizational objectives Staffing
Usually contrast to org objectives: deliver on time, limited budget
Do not show a good number in ROI
No clear quantifiable benefit for the organization
Staffing 
Perceived as second-class citizens
Morale therefore suffers
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17. 2. Management Issues Process Organizational aspects of maintenance
Similar to development process, but has unique activities
Organizational aspects of maintenance
Case-by-case policy in task delegation
Dedicated maintainer or a special team
Outsourcing 
Usually for less mission-critical systems
Challenges
Scope of maintenance and contractual details
Transition to outsourcer
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18. 3. Maintenance Cost Estimation
Parametric model
COCOMO for maintenance
Experience
Delphi study
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19. 4. Software Maintenance Measurement
Common categories
size; effort; schedule; and quality
Based on Maintainability characteristics
Analyzability: Measures of the maintainer's effort or resources expended in trying to diagnose deficiencies or causes of failure, or in identifying parts to be modified
Changeability: Measures of the maintainer's effort associated with implementing a specified modification
Stability: Measures of the unexpected behavior of software, including that encountered during testing
Testability: Measures of the maintainer's and users' effort in trying to test the modified software
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© 2011 USC-CSSE

20. Outline Software Maintenance Fundamentals
Key Issues in Software Maintenance
Maintenance Process
Techniques for Maintenance
03/02/2011
© 2011 USC-CSSE

21. The Incremental Commitment Spiral Model
This slide shows the overall concept of the ICM
Commitment and accountability
Success-critical stakeholder satisficing,
Incremental growth of system definition and stakeholder commitment,
Concurrent engineering,
Iterative development cycles,
Risk-based activity levels and milestones
Jan 11, 2011

22. Software Maintenance Process
Post-delivery stage
The IEEE Maintenance Process Activities
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23. Another Software Maintenance Process
ISO/IEC Software Maintenance Process
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24. Maintenance Activities
Unique Activity
Transition: a controlled and coordinated sequence of activities during which software is transferred progressively from the developer to the maintainer
Modification Request Acceptance/Rejection: modification request work over a certain size/effort/complexity may be rejected by maintainers and rerouted to a developer
Modification Request and Problem Report Help Desk: an end-user support function that triggers the assessment, prioritization, and costing of modification requests
Impact Analysis
Software Support: help and advice to users concerning a request for information (for example, business rules, validation, data meaning and ad-hoc requests/reports)
Service Level Agreements (SLAs) and specialized (domain-specific) maintenance contracts which are the responsibility of the maintainers
Supporting Activity
Maintenance planning activity
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25. Maintenance Activities
Unique Activity
Supporting Activity
software maintenance planning
software configuration management,
verification and validation,
software quality assurance, reviews, audits
user training and maintainer training
Maintenance planning activity
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26. Maintenance Activities
Unique Activity
Supporting Activity
Maintenance planning activity
Business planning (organizational level)
Maintenance planning (transition level)
Release/version planning (software level)
Individual software change request planning (request level)
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27. Release/version planning activity
Collect the dates of availability of individual requests
Agree with users on the content of subsequent releases/versions
Identify potential conflicts and develop alternatives
Assess the risk of a given release and develop a back-out plan in case problems should arise
Inform all the stakeholders
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28. Software configuration management
Critical element of the maintenance process
For
verification, validation,
audit of each step required to identify, authorize, implement, and release the software product.
Track Modification Requests or Problem Reports
Control the changes
Different from CM of software development
03/02/2011
© 2011 USC-CSSE

29. Outline Software Maintenance Fundamentals
Key Issues in Software Maintenance
Maintenance Process
Techniques for Maintenance
03/02/2011
© 2011 USC-CSSE

30. Techniques for Maintenance
Program Comprehension
reading and understanding programs in order to implement changes.
Code browsers are key tools for program comprehension.
Need clear and concise documentation
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31. Techniques for Maintenance
Reengineering 
examination and alteration of software to reconstitute it in a new form, and includes the subsequent implementation of the new form
the most radical (and expensive) form of alteration
It is often not undertaken to improve maintainability, but to replace aging legacy software
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32. Techniques for Maintenance
Reverse engineering
Analyzing software to identify the software's components and their interrelationships and to create representations of the software in another form or at higher levels of abstraction
Reverse engineering is passive;
it does not change the software, or result in new software
E.g. redocumentation, design recovery, refactoring (to improve performance), data reverse engineering (logical schemas are recovered from physical databases)
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33. Distribution of Maintenance Problem Items
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35. References
[Lientz 1981] Lientz, B.P. & Swanson, E. (1981). "Problems in application software maintenance". Communications of the ACM 24 (11),
[SWEBOK 2004] Software Engineering Body of Knowledge version
03/02/2011
© 2011 USC-CSSE