PROF. SUJIT H. KARANDE

1. Chapter No. 5
Maintenance
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2. Study Resources:
Reference Books
• Analysis and design of information systems: James A. Senn.
Page no. 694
• System Analysis And Design: Jalote. Page No. 11
• Software Engineering : Pressman. Page No. 762
• Software Engineering Concepts: Richard Fairley. Page No. 311-
328
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3. 5.1. Types of Maintenance
The process of changing of a system after it
has been delivered and is in use is called
Software maintenance.
• Why maintenance is required:
• Not as rewarding as exciting as developing systems. It is
perceived as requiring neither skill nor experience.
• Users are not fully cognizant of the maintenance problem or
its high cost.
• Few tools and techniques are available for maintenance.
• A good test plan is lacking.
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4. 5.1. Types of Maintenance
Why maintenance is required:
• Standards, procedures, and guidelines are poorly defined
and enforced.
• Maintenance is viewed as a necessary evil, often delegated
to junior programmers. There are practically no
maintenance manager job classification in the MIS field.
• Programs are often maintained without care for structure
and documentation.
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5. 5.1. Types of Maintenance
Types of software maintenance
1. Corrective maintenance
2. Adaptive maintenance
3. Perfective maintenance
4. Preventive maintenance
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6. 1. Corrective maintenance
• Maintenance which is required when an item has
failed or worn out, to bring it back to working
order.
• In most cases this is expensive.
• When equipment fails, need to replace, coding
errors.
• Cost of this type of maintenance is must not
greater that preventive maintenance.
• Is concern with fixing reported errors in the
software.
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7. 2. Adaptive maintenance
• Changing the s/f to new environment i.e.
changing h/w platform, operating system.
• Addition of new features, capabilities, up
gradations, new requirements, new problems.
• Isolation of system-dependent features.
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8. 3. Perfective maintenance
• Perfective maintenance involves implementing
new functional or non-functional system
requirements.
• Enhance the system by improving efficiency,
reliability, functionality, or maintainability.
• Corrective and adaptive maintenance are reactive.
• Perfective maintenance, in contract, is proactive.
• The idea is to fix the system before it breaks
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9. 4. Preventive maintenance
• The objective of preventive maintenance is to
anticipate problems and correct them before
they occur.
• System performance monitoring is an
important key to preventive maintenance.
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10. 5.2. Maintenance Cost
Software maintenance costs around 50% of total
software life-cycle cost.
How to reduce maintenance cost:
• Maintenance management audit
• Software system audit
• Software modification
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11. Maintenance management audit
• This evaluates the quality of maintenance
effort .
• Follow-up of all requests of maintenance.
• Total hours worked are spent on error
corrections, addition/changes/deletions, and
improvements.
• Organization must have a well-defined
maintenance reduction program.
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12. Software system audit
1. Overall view of the system documents and an
assessment of the quality of data files and data
bases and system maintainability, reliability and
efficiency.
2. Determination of functionality and assignment of
preliminary ranking value.
3. Detail program audit – ranking value, mean time
between failure(MTBF), size of the maintenance
backlog. This determines system availability to
users.
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13. Software modification
1. Program rewrites , which includes logic
simplification, documentation updates, error
correction.
2. System level updates, which includes system
level documentations, up to date DFDs or
system flowcharts, cross- references
programs.
3. Reaudit of low-ranking programs to make
sure that the errors have been corrected.
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14. 5.3. Reverse Engineering
• Process of creating specifications that describe the action
of existing applications.
• Reverse engineering can also be performed to recreate the
information describing the intent of existing systems.
• Reverse engineering is an important concept that fits with
evolution of information systems.
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15. 5.3. What is Reverse Engineering ?
Forward Engineering
Requirements
Design
Source Code
Behavior
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16. 5.3. What is Reverse Engineering ?
Forward Engineering Reverse Engineering
Requirements
Design
Source Code
Behavior
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17. 5.3. What is Reverse Engineering?
1. A systematic methodology for analyzing the design of an
existing device or system, either as an approach to study
the design or as a prerequisite for re-design.
2. Is the process of analysing a subject system to identify the
system’s components and their interrelationships and
create representations of the system in another form or at
a higher level of abstraction.
— Chikofsky & Cross, 1990
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18. 5.3. What is Reverse Engineering?
3. Analysing software with a view to understanding its
design and specification
4. May be part of a re-engineering process but may also be
used to re-specify a system for re-implementation
5. Builds a program data base and generates information
from this
6. Program understanding tools (browsers, cross-reference
generators, etc.) may be used in this process
7. To derive design information at the highest level possible
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19. Software Reengineering Process
Program Modularised Original data
Original
documentation program
program
Reverse
engineering
Data
Source code Program reengineering
translation modularisation
Program
structure
improvement
Structured Reengineered
program data
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20. The Reverse Engineering Process
Program stucture
Automated diagrams
analysis
System
System to be Document Data stucture
information
re-engineered generation diagrams
store
Manual
annotation Traceability
matrices
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21. The Reverse Engineering Process
1. Collect Information
2. Examine Information
3. Extract the Structure
4. Record Functionality
5. Record Data-flow
6. Record Control-flow
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22. 5.3. What is Reverse Engineering?
Abstraction System
Reverse Engineering Forward Engineering
Abstraction Re-Implementation
Old system New System
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23. 5.3. What is Reverse Engineering?
• RE encompasses any activity that is done to
determine how a product works, to learn the
ideas and technology that were used in
developing that product.
• RE can be done at many levels
• RE generally belongs to Software
Maintenance
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24. 5.3. Difference - Reverse Engineering &
Reengineering
• Reverse engineering is the general process of analyzing a
technology specifically to ascertain how it was designed or how
it operates. This kind of inquiry engages individuals in a
constructive learning process about the operation of systems
and products.
• Reverse engineering as a method is not confined to any
particular purpose, but is often an important part of the scientific
method and technological development.
• Reverse-engineering is taking apart a finished product for the
purposes of learning how it works.
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25. 5.3. Difference - Reverse Engineering &
Reengineering
• Re-engineering is the bridge used by legacy software to
migrate to an organization’s new maintenance
environment.
• Less formally, Re-engineering is the modification of a
software system that takes place after it has been reverse
engineered, generally to add new functionality, or to
correct errors.
• Re-engineering is simply a new re-implementation of a
product with better engineering. 25

26. 5.3. Difference - Reverse Engineering &
Reengineering
• Reverse engineering is to take a bridge
apart (separately) to see how it was built.
• Re-engineering is to throw a bridge away
and rebuild it from scratch.
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27. 5.3. Why do we need RE ?
• Recovery of lost information
– providing proper system documentation
• Assisting with maintenance
– identification of side effects and anomalies
• Migration to another hw/sw platform
• Facilitating software reuse
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28. 5.3. Why do we need RE ?
• Benefits
– maintenance cost savings
– quality improvements
– competitive advantages
– software reuse facilitation
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29. Scope and Task of Reverse Engineering
• program understanding
Problem/Application
domain
Mapping
Program/Implemen.
domain
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30. Scope and Task of Reverse Engineering
• Redocumentation and/or document
generation
• Recovery of design approach and design
details at any level of abstraction
• Identifying reusable components and
components that need restructuring
• Recovering business rules
• Understanding high-level system description.
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31. Levels of abstractions
• Application
– Application concepts, business rule, policies
• Function
– Logical and functional specification, non-functional
requirement
• Structure
– Data and control flow, dependency graphs
– Structure and subsystem charts
– Architectures
• Implementation
– Symbol tables, source text
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32. 5.3. Reverse Engineering
•Reverse engineering is required because of
•To understand data
•To understand processing
•To modify user interface
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33. 5.3. Reverse Engineering
Processes of Reverse Engineering:
1. Abstraction level
2. Completeness
3. Directionality
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34. 5.4. Introduction to legacy systems
• Legacy systems are considered to be potentially problematic by many
software engineers for several reasons.
• These systems can be hard to maintain, improve, and expand because
there is a general lack of understanding of the system .
• A legacy system is an antiquated (OLD FACHIONED) computer system
or application program which continues to be used because the user
(typically an organization) does not want to replace or redesign it.
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35. 5.4. Introduction to legacy systems
• An old method, technology, computer system, or application
program.
• Continues to be used, typically because it still functions for
the users' needs, even though newer technology or more
efficient methods of performing a task are now available .
• Older software systems that remain vital to an organisation.
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36. 5.4. Introduction to legacy systems
• These systems are often hard to maintain, improve, and expand
because there is a general lack of understanding of the system;
• The designers of the system have left the organization, so there is
no one left to explain how it works.
• Lack of understanding can be exacerbated by inadequate
documentation, or manuals getting lost over the years.
• Integration with newer systems may also be difficult because new
software may use completely different technologies.
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37. 5.4. Introduction to legacy systems
Despite these problems, organizations can have compelling reasons for
keeping a legacy system, such as:
1. The costs of redesigning the system are prohibitive because it is
large, monolithic, and/or complex.
2. The system requires close to 100% availability, so it cannot be
taken out of service, and the cost of designing a new system with a
similar availability level are high.
3. The way the system works is not well understood. Such a situation
can occur when the designers of the system have left the
organization, and the system has either not been fully documented
or such documentation has been lost over the years.
4. The user expects that the system can easily be replaced when this
becomes necessary.
5. The system works satisfactorily, and the owner sees no reason for
changing it.
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38. 5.5. Role of documentation in maintenance and
types of documentation.
• It is one of the oldest recommended practices and yet has
been, and continues to be, renowned for its absence.
• Software maintenance is traditionally defined as any
modification made on a software system after its delivery.
• predominant activity in software engineering
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39. 5.5. TYPES OF DOCUMENTATION
• Types of documentation include:
• Requirements
• Architecture/Design
• Technical
• End User
• Marketing
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