SOFTWARE MAINTENANCE_______________________________________________________________
Overview
Software maintenance in software engineering is the modification
of a software product after delivery to correct faults, to improve
performance or other attributes.
A common perception of maintenance is that it merely involves
fixing defects. However, one study indicated that over 80% of
maintenance effort is used for non-corrective actions. This
perception is perpetuated by users submitting problem reports that
in reality are functionality enhancements to the system. More
recent studies put the bug-fixing proportion closer to 21%.
History
Software maintenance and evolution of systems were first
addressed by Meir M. Lehman in 1969. Over a period of twenty
years, his research led to the formulation of Lehman's Laws
(Lehman 1997). Key findings of his research include that
maintenance is really evolutionary development and that
maintenance decisions are aided by understanding what happens to
systems (and software) over time. Lehman demonstrated that
systems continue to evolve over time. As they evolve, they grow
more complex unless some action, such as code refactoring, is
taken to reduce the complexity.
In the late 1970s, a famous and widely cited survey study by
Lientz and Swanson, the very high fraction of life-cycle costs that
were being expended on maintenance was exposed. They
categorized maintenance activities into four classes:
Adaptive – modifying the system to cope with changes in
the software environment (DBMS, OS)
Perfective – implementing new or changed user
requirements which concern functional enhancements to
the software
Corrective – diagnosing and fixing errors, possibly ones
found by users
Preventive – increasing software maintainability or
reliability to prevent problems in the future
The survey showed that around 75% of the maintenance effort was
on the first two types, and error correction consumed about 21%.
Many subsequent studies suggest a similar magnitude of the
problem. Studies show that contribution of end user is crucial
during the new requirement data gathering and analysis. And this
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is the main cause of any problem during software evolution and
maintenance. So software maintenance is important because it
consumes a large part of the overall lifecycle costs and also the
inability to change software quickly and reliably means that
business opportunities are lost.
Importance of software maintenance
The key software maintenance issues are both managerial and
technical. Key management issues are:
1. Alignment with customer priorities;
2. Staffing;
3. Which organization does maintenance;
4. Estimating costs.
Key technical issues are:
1. Limited understanding;
2. Impact analysis;
3. Testing;
4. Maintainability measurement.
Software maintenance is a very broad activity that includes error
correction, enhancements of capabilities, deletion of obsolete
capabilities, and optimization. Because change is inevitable,
mechanisms must be developed for evaluation, controlling and
making modifications. The purpose is to preserve the value of
software over time. The value can be enhanced by expanding the
customer base, meeting additional requirements, making it easier
to use and more efficient and employing newer technology.
Maintenance may span for 20 years, whereas development may
last1-2 years.
Software maintenance planning
An integral part of software is the maintenance one, which requires
an accurate maintenance plan to be prepared during the software
development. It should specify how users will request
modifications or report problems. The budget should include
resource and cost estimates. A new decision should be addressed
for the developing of every new system feature and its quality
objectives. The software maintenance, which can last for 5–6 years
(or even decades) after the development process, calls for an
effective plan which can address the scope of software
maintenance, the tailoring of the post-delivery/deployment process,
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the designation of who will provide maintenance, and an estimate
of the life-cycle costs. The selection of proper enforcement of
standards is the challenging task right from early stage of software
engineering which has not got definite importance by the
concerned stakeholders.
Software maintenance processes
This section describes the six software maintenance processes as:
1. The implementation process contains software preparation and
transition activities, such as the conception and creation of the
maintenance plan; the preparation for handling problems identified
during development; and the follow-up on product configuration
management.
2. The problem and modification analysis process, which is executed
once the application has become the responsibility of the
maintenance group. The maintenance programmer must analyze
each request, confirm it (by reproducing the situation) and check
its validity, investigate it and propose a solution, document the
request and the solution proposal, and finally, obtain all the
required authorizations to apply the modifications.
3. The process considering the implementation of the modification
itself.
4. The process acceptance of the modification, by confirming the
modified work with the individual who submitted the request, in
order to make sure the modification provided a solution.
5. The migration process (platform migration, for example) is
exceptional, and is not part of daily maintenance tasks. If the
software must be ported to another platform without any change in
functionality, this process will be used and a maintenance project
team is likely to be assigned to this task.
6. Finally, the last maintenance process, also an event which does not
occur on a daily basis, is the retirement of a piece of software.
There are a number of processes, activities and practices that are
unique to maintainers. For example:
Transition: a controlled and coordinated sequence of activities
during which a system is transferred progressively from the
developer to the maintainer;
Service Level Agreements (SLAs) and specialized (domain-
specific) maintenance contracts negotiated by maintainers;
Modification Request and Problem Report Help Desk: a
problem-handling process used by maintainers to prioritize,
documents and route the requests they receive;
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Categories of maintenance in ISO/IEC 14764
E.B. Swanson initially identified three categories of maintenance:
corrective, adaptive, and perfective. These have since been updated
and ISO/IEC 14764 presents:
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.
There is also a notion of pre-delivery/pre-release maintenance
which is all the good things you do in order to lower the total cost
of ownership of the software. Things like compliance with coding
standards that includes software maintainability goals. The
management of coupling and cohesion of the software. The
attainment of software supportability goals (SAE JA1004, JA1005
and JA1006 for example). It is worth noting that some academic
institutions are carrying out research to quantify the cost to
ongoing software maintenance due to the lack of resources, such as
design documents and system/software comprehension training
and resources (multiply costs by approx. 1.5-2.0 where there is no
design data available).
Maintenance Factors
Impact of key adjustment factors on maintenance (sorted in order
of maximum positive impact)
Maintenance Factors Plus Range
Maintenance specialists 35%
High staff experience 34%
Table-driven variables and data 33%
Low complexity of base code 32%
Y2K and special search engines 30%
Code restructuring tools 29%
Re-engineering tools 27%
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High level programming languages 25%
Reverse engineering tools 23%
Complexity analysis tools 20%
Defect tracking tools 20%
Y2K “mass update” specialists 20%
Automated change control tools 18%
Unpaid overtime 18%
Quality measurements 16%
Formal base code inspections 15%
Regression test libraries 15%
Excellent response time 12%
Annual training of > 10 days 12%
High management experience 12%
HELP desk automation 12%
No error prone modules 10%
On-line defect reporting 10%
Productivity measurements 8%
Excellent ease of use 7%
User satisfaction measurements 5%
High team morale 5%
Sum 503%
Not only are error-prone modules troublesome, but many other
factors can degrade performance too. For example, very complex
“spaghetti code” is quite difficult to maintain safely. A very
common situation which often degrades performance is lack of
suitable maintenance tools, such as defect tracking software,
change management software, and test library software. Below
describe some of the factors and the range of impact on software
maintenance.
Impact of key adjustment factors on maintenance (sorted in order
of maximum negative impact)
Maintenance Factors Minus Range
Error prone modules -50%
Embedded variables and data -45%
Staff inexperience -40%
High code complexity -30%
No Y2K of special search engines -28%
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Manual change control methods -27%
Low level programming languages -25%
No defect tracking tools -24%
No Y2K “mass update” specialists -22%
Poor ease of use -18%
No quality measurements -18%
No maintenance specialists -18%
Poor response time -16%
No code inspections -15%
No regression test libraries -15%
No help desk automation -15%
No on-line defect reporting -12%
Management inexperience -15%
No code restructuring tools -10%
No annual training -10%
No reengineering tools -10%
No reverse-engineering tools -10%
No complexity analysis tools -10%
No productivity measurements -7%
Poor team morale -6%
No user satisfaction measurements -4%
No unpaid overtime 0%
Sum -500%
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