Chapter 5: Software Maintenance

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Acronyms
MR
Modification Request
PR
Problem Report
SCM
Software Configuration Management
SLA
Service-Level Agreement
SQA
Software Quality Assurance
V&V
Verification and Validation
Introduction

Software development efforts result in the delivery of a software product that satisfies user requirements. Accordingly, the software product must change or evolve. Once in operation, defects are uncovered, operating environments change, and new user requirements surface. The maintenance phase of the life cycle begins following a warranty period or postimplementation support delivery, but maintenance activities occur much earlier.

Software maintenance is an integral part of a software life cycle. However, it has not received the same degree of attention that the other phases have. Historically, software development has had a much higher profile than software maintenance in most organizations. This is now changing, as organizations strive to squeeze the most out of their software development investment by keeping software operating as long as possible. The open source paradigm has brought further attention to the issue of maintaining software artifacts developed by others.

In this Guide, software maintenance is defined as the totality of activities required to provide cost-effective support to software. Activities are performed during the predelivery stage as well as during the postdelivery stage. Predelivery activities include planning for postdelivery operations, maintainability, and logistics determination for transition activities [1*, c6s9]. Postdelivery activities include software modification, training, and operating or interfacing to a help desk.

The Software Maintenance knowledge area (KA) is related to all other aspects of software engineering. Therefore, this KA description is linked to all other software engineering KAs of the Guide.

Breakdown of Topics for Software Maintenance

The breakdown of topics for the Software Maintenance KA is shown in Figure 5.1.

1 Software Maintenance Fundamentals

This first section introduces the concepts and terminology that form an underlying basis to understanding the role and scope of software maintenance. The topics provide definitions and emphasize why there is a need for maintenance. Categories of software maintenance are critical to understanding its underlying meaning.

1.1 Definitions and Terminology

The purpose of software maintenance is defined in the international standard for software maintenance: ISO/IEC/IEEE 14764 [1*].1 In the context of software engineering, software maintenance is essentially one of the many technical processes.

The objective of software maintenance is to modify existing software while preserving its integrity. The international standard also states the importance of having some maintenance activities prior to the final delivery of software (predelivery activities). Notably, IEEE 14764 emphasizes the importance of the predelivery aspects of maintenance—planning, for example.

1.2 Nature of Maintenance

Software maintenance sustains the software product throughout its life cycle (from development to operations). Modification requests are logged and tracked, the impact of proposed changes is determined, code and other software artifacts are modified, testing is conducted, and a new version of the software product is released. Also, training and daily support are provided to users. The term maintainer is defined as an organization that performs maintenance activities. In this KA, the term will sometimes refer to individuals who perform those activities, contrasting them with the developers.

IEEE 14764 identifies the primary activities of software maintenance as process implementation, problem and modification analysis, modification implementation, maintenance review/acceptance, migration, and retirement. These activities are discussed in section 3.2, Maintenance Activities.

Maintainers can learn from the developers’ knowledge of the software. Contact with the developers and early involvement by the maintainer helps reduce the overall maintenance effort. In some instances, the initial developer cannot be reached or has moved on to other tasks, which creates an additional challenge for maintainers. Maintenance must take software artifacts from development (for example, code or documentation) and support them immediately, then progressively evolve/maintain them over a software life cycle.

1.3 Need for Maintenance

Maintenance is needed to ensure that the software continues to satisfy user requirements. Maintenance is applicable to software that is developed using any software life cycle model (for example, spiral or linear). Software products change due to corrective and noncorrective software actions. Maintenance must be performed in order to

  • correct faults;
  • improve the design;
  • implement enhancements;
  • interface with other software;
  • adapt programs so that different hardware, software, system features, and telecommunications facilities can be used;
  • migrate legacy software; and
  • retire software.

Five key characteristics comprise the maintainer’s activities:

  • maintaining control over the software’s day-to-day functions;
  • maintaining control over software modification;
  • perfecting existing functions;
  • identifying security threats and fixing security vulnerabilities; and
  • preventing software performance from degrading to unacceptable levels.

1.4 Majority of Maintenance Costs

Maintenance consumes a major share of the financial resources in a software life cycle. A common perception of software maintenance is that it merely fixes faults. However, studies and surveys over the years have indicated that the majority, over 80 percent, of software maintenance is used for noncorrective actions [2*, figure 4.1]. Grouping enhancements and corrections together in management reports contributes to some misconceptions regarding the high cost of corrections. Understanding the categories of software maintenance helps to understand the structure of software maintenance costs. Also, understanding the factors that influence the maintainability of software can help to contain costs. Some environmental factors and their relationship to software maintenance costs include the following:

  • Operating environment refers to hardware and software.
  • Organizational environment refers to policies, competition, process, product, and personnel.

1.5 Evolution of Software

Software maintenance in terms of evolution was first addressed in the late 1960s. Over a period of twenty years, research led to the formulation of eight “Laws of Evolution.” Key findings include a proposal that maintenance is evolutionary development and that maintenance decisions are aided by understanding what happens to software over time. Some state that maintenance is continued development, except that there is an extra input (or constraint)–in other words, existing large software is never complete and continues to evolve; as it evolves, it grows more complex unless some action is taken to reduce this complexity.

1.6 Categories of Maintenance

Three categories (types) of maintenance have been defined: corrective, adaptive, and perfective [2*, c4s3]. IEEE 14764 includes a fourth category–preventative.

  • Corrective maintenance: reactive modification (or repairs) of a software product performed after delivery to correct discovered problems. Included in this category is emergency maintenance, which is an unscheduled modification performed to temporarily keep a software product operational pending corrective maintenance.
  • Adaptive maintenance: modification of a software product performed after delivery to keep a software product usable in a changed or changing environment. For example, the operating system might be upgraded and some changes to the software may be necessary.
  • Perfective maintenance: modification of a software product after delivery to provide enhancements for users, improvement of program documentation, and recoding to

improve software performance, maintainability, or other software attributes.

  • Preventive maintenance: modification of a software product after delivery to detect and correct latent faults in the software product before they become operational faults.

IEEE 14764 classifies adaptive and perfective maintenance as maintenance enhancements. It also groups together the corrective and preventive maintenance categories into a correction category, as shown in Table 5.1.

Table 5.1. Software Maintenance Categories
Correction Enhancement
Proactive Preventive Perfective
Reactive Corrective Adaptive

2 Key Issues in Software Maintenance

A number of key issues must be dealt with to ensure the effective maintenance of software. Software maintenance provides unique technical and management challenges for software engineers—for example, trying to find a fault in software containing a large number of lines of code that another software engineer developed. Similarly, competing with software developers for resources is a constant battle. Planning for a future release, which often includes coding the next release while sending out emergency patches for the current release, also creates a challenge. The following section presents some of the technical and management issues related to software maintenance. They have been grouped under the following topic headings:

  • technical issues,
  • management issues,
  • cost estimation, and
  • measurement.

2.1 Technical Issues

2.1.1 Limited Understanding

Limited understanding refers to how quickly a software engineer can understand where to make a change or correction in software that he or she did not develop. Research indicates that about half of the total maintenance effort is devoted to understanding the software to be modified. Thus, the topic of software comprehension is of great interest to software engineers. Comprehension is more difficult in text-oriented representation—in source code, for example—where it is often difficult to trace the evolution of software through its releases/ versions if changes are not documented and if the developers are not available to explain it, which is often the case. Thus, software engineers may initially have a limited understanding of the software; much has to be done to remedy this.

2.1.2 Testing

The cost of repeating full testing on a major piece of software is significant in terms of time and money. In order to ensure that the requested problem reports are valid, the maintainer should replicate or verify problems by running the appropriate tests. Regression testing (the selective retesting of software or a component to verify that the modifications have not caused unintended effects) is an important testing concept in maintenance. Additionally, finding time to test is often difficult. Coordinating tests when different members of the maintenance team are working on different problems at the same time remains a challenge. When software performs critical functions, it may be difficult to bring it offline to test. Tests cannot be executed in the most meaningful place–the production system. The Software Testing KA provides additional information and references on this matter in its subtopic on regression testing.

2.1.3 Impact Analysis

Impact analysis describes how to conduct, costeffectively, a complete analysis of the impact of a change in existing software. Maintainers must possess an intimate knowledge of the software’s structure and content. They use that knowledge to perform impact analysis, which identifies all systems and software products affected by a software change request and develops an estimate of the resources needed to accomplish the change. Additionally, the risk of making the change is determined. The change request, sometimes called a modification request (MR) and often called a problem report (PR), must first be analyzed and translated into software terms. Impact analysis is performed after a change request enters the software configuration management process. IEEE 14764 states the impact analysis tasks:

• analyze MRs/PRs; • replicate or verify the problem;

  • develop options for implementing the modification;
  • document the MR/PR, the results, and the execution options;
  • obtain approval for the selected modification option.

The severity of a problem is often used to decide how and when it will be fixed. The software engineer then identifies the affected components. Several potential solutions are provided, followed by a recommendation as to the best course of action.

Software designed with maintainability in mind greatly facilitates impact analysis. More information can be found in the Software Configuration Management KA.

2.1.4 Maintainability

IEEE 14764 [1*, c3s4] defines maintainability as the capability of the software product to be modified. Modifications may include corrections, improvements, or adaptation of the software to changes in environment as well as changes in requirements and functional specifications.

As a primary software quality characteristic, maintainability should be specified, reviewed, and controlled during software development activities in order to reduce maintenance costs. When done successfully, the software’s maintainability will improve. Maintainability is often difficult to achieve because the subcharacteristics are often not an important focus during the process of software development. The developers are, typically, more preoccupied with many other activities and frequently prone to disregard the maintainer’s requirements. This in turn can, and often does, result in a lack of software documentation and test environments, which is a leading cause of difficulties in program comprehension and subsequent impact analysis. The presence of systematic and mature processes, techniques, and tools helps to enhance the maintainability of software.

2.2 Management Issues

2.2.1 Alignment with Organizational Objectives

Organizational objectives describe how to demonstrate the return on investment of software maintenance activities. Initial software development is usually project-based, with a defined time scale and budget. The main emphasis is to deliver a product that meets user needs on time and within budget. In contrast, software maintenance often has the objective of extending the life of software for as long as possible. In addition, it may be driven by the need to meet user demand for software updates and enhancements. In both cases, the return on investment is much less clear, so that the view at the senior management level is often that of a major activity consuming significant resources with no clear quantifiable benefit for the organization.

2.2.2 Staffing

Staffing refers to how to attract and keep software maintenance staff. Maintenance is not often viewed as glamorous work. As a result, software maintenance personnel are frequently viewed as “second-class citizens,” and morale therefore suffers.

2.2.3 Process

The software life cycle process is a set of activities, methods, practices, and transformations that people use to develop and maintain software and its associated products. At the process level, software maintenance activities share much in common with software development (for example, software configuration management is a crucial activity in both). Maintenance also requires several activities that are not found in software development (see section 3.2 on unique activities for details). These activities present challenges to management.

2.2.4 Organizational Aspects of Maintenance

Organizational aspects describe how to identify which organization and/or function will be responsible for the maintenance of software. The team that develops the software is not necessarily assigned to maintain the software once it is operational.

In deciding where the software maintenance function will be located, software engineering organizations may, for example, stay with the original developer or go to a permanent maintenance- specific team (or maintainer). Having a permanent maintenance team has many benefits:

  • allows for specialization;
  • creates communication channels;
  • promotes an egoless, collegiate atmosphere;
  • reduces dependency on individuals;
  • allows for periodic audit checks.

Since there are many pros and cons to each option, the decision should be made on a case-bycase basis. What is important is the delegation or assignment of the maintenance responsibility to a single group or person, regardless of the organization’s structure.

2.2.5 Outsourcing

Outsourcing and offshoring software maintenance has become a major industry. Organizations are outsourcing entire portfolios of software, including software maintenance. More often, the outsourcing option is selected for less mission-critical software, as organizations are unwilling to lose control of the software used in their core business. One of the major challenges for outsourcers is to determine the scope of the maintenance services required, the terms of a service- level agreement, and the contractual details. Outsourcers will need to invest in a maintenance infrastructure, and the help desk at the remote site should be staffed with native-language speakers. Outsourcing requires a significant initial investment and the setup of a maintenance process that will require automation.

2.3 Maintenance Cost Estimation

Software engineers must understand the different categories of software maintenance, discussed above, in order to address the question of estimating the cost of software maintenance. For planning purposes, cost estimation is an important aspect of planning for software maintenance.

2.3.1 Cost Estimation

Section 2.1.3 describes how impact analysis identifies all systems and software products affected by a software change request and develops an estimate of the resources needed to accomplish that change.

Maintenance cost estimates are affected by many technical and nontechnical factors. IEEE 14764 states that “the two most popular approaches to estimating resources for software maintenance are the use of parametric models and the use of experience” [1*, c7s4.1]. A combination of these two can also be used.

2.3.2 Parametric Models

Parametric cost modeling (mathematical models) has been applied to software maintenance. Of significance is that historical data from past maintenance are needed in order to use and calibrate the mathematical models. Cost driver attributes affect the estimates.

2.3.3 Experience

Experience, in the form of expert judgment, is often used to estimate maintenance effort. Clearly, the best approach to maintenance estimation is to combine historical data and experience. The cost to conduct a modification (in terms of number of people and amount of time) is then derived. Maintenance estimation historical data should be provided as a result of a measurement program.

2.4 Software Maintenance Measurement

Entities related to software maintenance, whose attributes can be subjected to measurement, include process, resource, and product [2*, c12s3.1].

There are several software measures that can be derived from the attributes of the software, the maintenance process, and personnel, including size, complexity, quality, understandability, maintainability, and effort. Complexity measures of software can also be obtained using available commercial tools. These measures constitute a good starting point for the maintainer’s measurement program. Discussion of software process and product measurement is also presented in the Software Engineering Process KA. The topic of a software measurement program is described in the Software Engineering Management KA.

2.4.1 Specific Measures

The maintainer must determine which measures are appropriate for a specific organization based on that organization’s own context. The software quality model suggests measures that are specific for software maintenance. Measures for subcharacteristics of maintainability include the following [4*, p. 60]:

  • Analyzability: measures of the maintainer’s effort or resources expended in trying either to diagnose deficiencies or causes of failure or to identify 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.
  • Other measures that maintainers use include
  • size of the software,
  • complexity of the software ,
  • understandability, and
  • maintainability.

Providing software maintenance effort, by categories, for different applications provides business information to users and their organizations. It can also enable the comparison of software maintenance profiles internally within an organization.

3 Maintenance Process

3.1 Maintenance Processes

3.2 Maintenance Activities

3.2.1 Unique Activities

3.2.2 Supporting Activities

3.2.3 Maintenance Planning Activities

3.2.4 Software Configuration Management

3.2.5 Software Quality

4 Techniques for Maintenance

4.1 Program Comprehension

4.2 Reengineering

4.3 Reverse Engineering

4.4 Migration

4.5 Retirement

5 Software Maintenance Tools

References

[1] IEEE Std., 14764-2006 (a.k.a.ISO/IEC 14764:2006) Standard for Software Engineering—Software Life Cycle Processes-Maintenance, IEEE, 2006.

[2] P. Grubb and A.A. Takang, Software Maintenance: Concepts and Practice, 2th ed., World Scientific Publishing, 2003.

[3] H.M. Sneed, "Offering Software Maintenance as an Offshore Service", Proc. IEEE Int'l Conf. Software Maintenance (ICSM 08), IEEE, 2008, pp. 1–5.

[4] J.W. Moore, The Road Map to Software Engineering: A Standards-Based Guide, Wiley-IEEE Computer Society Press, 2006.

[5] IEEE, ISO/IEC/IEEE 24765:2010 Systems and Software Engineering—Vocabulary, ISO/IEC/IEEE, IEEE, 2010.

[6] A. April and A. Abran, Software Maintenance Management: Evaluation and Continuous Improvement, Wiley-IEEE Computer Society Press, 2008.

[7] M. Kajko-Mattsson, Towards a Business Maintenance Model, Proc. Int’l Conf. Software Maintenance, IEEE, 2001, pp. 500–509.