Software Engineering Body of Knowledge (v3) (2014) (811503), страница 27
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Planning for afuture release, which often includes coding thenext release while sending out emergency patchesfor the current release, also creates a challenge.The following section presents some of the technical and management issues related to softwaremaintenance. They have been grouped under thefollowing topic headings:• technical issues,• management issues,• cost estimation, and• measurement.2.1. Technical Issues2.1.1. Limited Understanding[2*, c6]Limited understanding refers to how quickly asoftware engineer can understand where to makea change or correction in software that he or shedid not develop. Research indicates that about halfof the total maintenance effort is devoted to understanding the software to be modified.
Thus, thetopic of software comprehension is of great interest to software engineers. Comprehension is moredifficult in text-oriented representation—in sourcecode, for example—where it is often difficult totrace the evolution of software through its releases/versions if changes are not documented and if thedevelopers are not available to explain it, which isoften 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[1*, c6s2.2.2] [2*, c9]The cost of repeating full testing on a majorpiece of software is significant in terms of timeand money. In order to ensure that the requestedproblem reports are valid, the maintainer shouldreplicate or verify problems by running theappropriate 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 inmaintenance. Additionally, finding time to test isoften difficult. Coordinating tests when differentmembers of the maintenance team are workingSoftware Maintenance 5-5on different problems at the same time remains achallenge. 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 SoftwareTesting KA provides additional information andreferences on this matter in its subtopic on regression testing.2.1.3. Impact Analysis[1*, c5s2.5] [2*, c13s3]Impact analysis describes how to conduct, costeffectively, a complete analysis of the impact ofa change in existing software. Maintainers mustpossess an intimate knowledge of the software’sstructure and content.
They use that knowledgeto perform impact analysis, which identifies allsystems and software products affected by a software change request and develops an estimate ofthe resources needed to accomplish the change.Additionally, the risk of making the change isdetermined. The change request, sometimes calleda modification request (MR) and often called aproblem report (PR), must first be analyzed andtranslated into software terms. Impact analysis isperformed after a change request enters the software configuration management process.
IEEE14764 states the impact analysis tasks:• analyze MRs/PRs;• replicate or verify the problem;• develop options for implementing themodification;• document the MR/PR, the results, and theexecution options;• obtain approval for the selected modificationoption.The severity of a problem is often used todecide 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 bestcourse of action.Software designed with maintainability in mindgreatly facilitates impact analysis.
More information can be found in the Software ConfigurationManagement KA.2.1.4. Maintainability[1*, c6s8] [2*, c12s5.5]IEEE 14764 [1*, c3s4] defines maintainabilityas the capability of the software product to bemodified. Modifications may include corrections,improvements, or adaptation of the software tochanges in environment as well as changes inrequirements and functional specifications.As a primary software quality characteristic,maintainability should be specified, reviewed, andcontrolled during software development activities in order to reduce maintenance costs. Whendone successfully, the software’s maintainabilitywill improve.
Maintainability is often difficult toachieve because the subcharacteristics are oftennot an important focus during the process of software development. The developers are, typically,more preoccupied with many other activities andfrequently prone to disregard the maintainer’srequirements. This in turn can, and often does,result in a lack of software documentation and testenvironments, which is a leading cause of difficulties in program comprehension and subsequentimpact analysis. The presence of systematic andmature processes, techniques, and tools helps toenhance the maintainability of software.2.2. Management Issues2.2.1. Alignment with OrganizationalObjectives[2*, c4]Organizational objectives describe how to demonstrate the return on investment of software maintenance activities.
Initial software development isusually project-based, with a defined time scale andbudget. The main emphasis is to deliver a productthat meets user needs on time and within budget.In contrast, software maintenance often has theobjective of extending the life of software for aslong as possible. In addition, it may be driven bythe need to meet user demand for software updatesand enhancements. In both cases, the return oninvestment is much less clear, so that the view atthe senior management level is often that of a majoractivity consuming significant resources with noclear quantifiable benefit for the organization.5-6 SWEBOK® Guide V3.02.2.2. Staffing[2*, c4s5, c10s4]Staffing refers to how to attract and keep software maintenance staff.
Maintenance is not oftenviewed as glamorous work. As a result, softwaremaintenance personnel are frequently viewedas “second-class citizens,” and morale thereforesuffers.2.2.3. Process[1*, c5] [2*, c5]The software life cycle process is a set of activities,methods, practices, and transformations that people use to develop and maintain software and itsassociated products. At the process level, softwaremaintenance activities share much in commonwith software development (for example, softwareconfiguration management is a crucial activity inboth).
Maintenance also requires several activitiesthat are not found in software development (seesection 3.2 on unique activities for details). Theseactivities present challenges to management.2.2.4. Organizational Aspects of Maintenance[1*, c7s2.3] [2*, c10]Organizational aspects describe how to identify which organization and/or function will beresponsible for the maintenance of software. Theteam that develops the software is not necessarily assigned to maintain the software once it isoperational.In deciding where the software maintenancefunction will be located, software engineeringorganizations may, for example, stay with theoriginal developer or go to a permanent maintenance-specific team (or maintainer). Having apermanent 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 eachoption, the decision should be made on a case-bycase basis.
What is important is the delegation orassignment of the maintenance responsibility to asingle group or person, regardless of the organization’s structure.2.2.5. Outsourcing[3*]Outsourcing and offshoring software maintenance has become a major industry. Organizations are outsourcing entire portfolios of software, including software maintenance. Moreoften, the outsourcing option is selected for lessmission-critical software, as organizations areunwilling to lose control of the software used intheir core business.
One of the major challengesfor outsourcers is to determine the scope of themaintenance services required, the terms of a service-level agreement, and the contractual details.Outsourcers will need to invest in a maintenanceinfrastructure, and the help desk at the remote siteshould be staffed with native-language speakers.Outsourcing requires a significant initial investment and the setup of a maintenance process thatwill require automation.2.3. Maintenance Cost EstimationSoftware engineers must understand the differentcategories of software maintenance, discussedabove, in order to address the question of estimating the cost of software maintenance. For planning purposes, cost estimation is an importantaspect of planning for software maintenance.2.3.1. Cost Estimation[2*, c7s2.4]Section 2.1.3 describes how impact analysis identifies all systems and software products affectedby a software change request and develops anestimate of the resources needed to accomplishthat change.Maintenance cost estimates are affectedby many technical and nontechnical factors.IEEE 14764 states that “the two most popularapproaches to estimating resources for softwaremaintenance are the use of parametric modelsand the use of experience” [1*, c7s4.1].
A combination of these two can also be used.Software Maintenance 5-72.3.2. Parametric Models[2*, c12s5.6]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 calibratethe mathematical models. Cost driver attributesaffect the estimates.2.3.3. Experience[2*, c12s5.5]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 termsof number of people and amount of time) is thenderived. Maintenance estimation historical datashould be provided as a result of a measurementprogram.2.4. Software Maintenance Measurement[1*, c6s5] [2*, c12]Entities related to software maintenance, whoseattributes can be subjected to measurement,include process, resource, and product [2*,c12s3.1].There are several software measures that canbe derived from the attributes of the software,the maintenance process, and personnel, including size, complexity, quality, understandability,maintainability, and effort.
Complexity measuresof software can also be obtained using availablecommercial tools. These measures constitute agood starting point for the maintainer’s measurement program. Discussion of software processand product measurement is also presented in theSoftware Engineering Process KA. The topic ofa software measurement program is described inthe Software Engineering Management KA.2.4.1. Specific Measures[2*, c12]The maintainer must determine which measuresare appropriate for a specific organization basedon that organization’s own context.
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