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Software Maintenance in software engineering is the modification of a software product after delivery to correct faults, to improve performance or other attributes.[1]
A common perception of maintenance is that it merely involves fixing defects. However, one study indicated that the majority, over 80%, of the maintenance effort is used for non-corrective actions (Pigosky 1997). This perception is perpetuated by users submitting problem reports that in reality are functionality enhancements to the system.
Software maintenance and evolution of systems was 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.
The key software maintenance issues are both managerial and technical. Key management issues are: alignment with customer priorities, staffing, which organization does maintenance, estimating costs. Key technical issues are: limited understanding, impact analysis, testing, maintainability measurement.
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In the late 1970s, a famous and widely cited survey study by Lientz and Swanson, exposed the very high fraction of life-cycle costs that were being expended on maintenance. They categorized maintenance activities into four classes:
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 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. [2] [3] [4]
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% |
| 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% |
| 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% |
The integral part of software is the maintenance part which requires accurate maintenance plan to be prepared during software development and should specify how users will request modifications or report problems and the estimation of resources such as cost should be included in the budget and a new decision should address to develop a new system and its quality objectives [1].The software maintenance which can last for 5–6 years after the development calls for an effective planning which addresses the scope of software maintenance, the tailoring of the post delivery process, the designation of who will provide maintenance, an estimate of the life-cycle costs [2].
This section describes the six software maintenance processes as:
There are a number of processes, activities and practices that are unique to maintainers, for example:
E.B. Swanson initially identified three categories of maintenance: corrective, adaptive, and perfective.[6] These have since been updated and ISO/IEC 14764 presents:
There is also a notion of pre-delivery/pre-release maintenance which is all the good things you do 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). Note also 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.).
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