Chapter 6: Software Configuration Management

Acronyms

CCB

Configuration Control Board

CM

Configuration Management

FCA

Functional Configuration Audit

PCA

Physical Configuration Audit

SCCB

Software Configuration Control Board

SCI

Software Configuration Item

SCM

Software Configuration Management

SCMP

Software Configuration Management Plan

SCR

Software Change Request

SCSA

Systems Modeling Language

SDD

Software Design Document

SEI/CMMI

Software Engineering Institute’s Capability Maturity Model Integration

SQA

Software Quality Assurance

SRS

Software Requirement Specification

INTRODUCTION A system can be defined as the combination of interacting elements organized to achieve one or more stated purposes [1]. The configuration of a system is the functional and physical characteris - tics of hardware or software as set forth in techni - cal documentation or achieved in a product [1]; it can also be thought of as a collection of specific versions of hardware, firmware, or software items combined according to specific build procedures to serve a particular purpose. Configuration man - agement (CM), then, is the discipline of identify - ing the configuration of a system at distinct points in time for the purpose of systematically control - ling changes to the configuration and maintaining the integrity and traceability of the configuration throughout the system life cycle. It is formally defined as A discipline applying technical and admin - istrative direction and surveillance to: iden - tify and document the functional and physi - cal characteristics of a configuration item, control changes to those characteristics, record and report change processing and implementation status, and verify compli - ance with specified requirements. [1] Software configuration management (SCM) is a supporting-software life cycle process that benefits project management, development and maintenance activities, quality assurance activi - ties, as well as the customers and users of the end product. The concepts of configuration management apply to all items to be controlled, although there are some differences in implementation between hardware CM and software CM. SCM is closely related to the software qual - ity assurance (SQA) activity. As defined in the Software Quality knowledge area (KA), SQA processes provide assurance that the software products and processes in the project life cycle conform to their specified requirements by plan - ning, enacting, and performing a set of activities to provide adequate confidence that quality is being built into the software. SCM activities help in accomplishing these SQA goals. In some proj - ect contexts, specific SQA requirements prescribe certain SCM activities 6-4 SWEBOK® Guide

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roles to be involved in the SCM process need to be clearly identified. Specific responsibilities for given SCM activities or tasks also need to be assigned to organizational entities, either by title or by organizational element. The overall author - ity and reporting channels for SCM should also be identified, although this might be accomplished at the project management or quality assurance planning stage. 1.3.2. SCM Resources and Schedules [2*, ann. Ds8] [3*, c23] Planning for SCM identifies the staff and tools involved in carrying out SCM activities and tasks. It addresses scheduling questions by establishing necessary sequences of SCM tasks and identify - ing their relationships to the project schedules and milestones established at the project manage - ment planning stage. Any training requirements necessary for implementing the plans and train - ing new staff members are also specified. 1.3.3. Tool Selection and Implementation [3*, c26s2, c26s6] [4*, c29s5] As for any area of software engineering, the selection and implementation of SCM tools should be carefully planned. The following ques - tions should be considered: • Organization: what motivates tool acquisi - tion from an organizational perspective? • Tools: can we use commercial tools or develop them ourselves? • Environment: what are the constraints imposed by the organization and its techni - cal context? • Legacy: how will projects use (or not) the new tools? • Financing: who will pay for the tools’ acquisition, maintenance, training, and customization? • Scope: how will the new tools be deployed— for instance, through the entire organization or only on specific projects? • Ownership: who is responsible for the intro - duction of new tools? • Future: what is the plan for the tools’ use in the future? • Change: how adaptable are the tools? • Branching and merging: are the tools’ capa - bilities compatible with the planned branch - ing and merging strategies? • Integration: do the various SCM tools inte - grate among themselves? With other tools in use in the organization? • Migration: can the repository maintained by the version control tool be ported to another version control tool while maintaining com - plete history of the configuration items it contains? SCM typically requires a set of tools, as opposed to a single tool. Such tool sets are some - times referred to as workbenches. In such a con - text, another important consideration in plan - ning for tool selection is determining if the SCM workbench will be open

(in other words, tools 

from different suppliers will be used in differ - ent activities of the SCM process) or integrated (where elements of the workbench are designed to work together). The size of the organization and the type of projects involved may also impact tool selection (see topic 7, Software Configuration Manage - ment Tools). 1.3.4. Vendor/Subcontractor Control [2*, c13] [3*, c13s9, c14s2] A software project might acquire or make use of purchased software products, such as compilers or other tools. SCM planning considers if and how these items will be taken under configura - tion control (for example, integrated into the proj - ect libraries) and how changes or updates will be evaluated and managed. Similar considerations apply to subcontracted software. When using subcontracted software, both the SCM requirements to be imposed on the subcontractor’s SCM process as part of the subcontract and the means for monitoring com - pliance need to be established. The latter includes consideration of what SCM information must be available for effective compliance monitoring. 6-6 SWEBOK® Guide

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insights leading to process changes and corre - sponding updates to the SCMP. Software libraries and the various SCM tool capabilities provide sources for extracting infor - mation about the characteristics of the SCM process (as well as providing project and man - agement information). For example, information about the time required to accomplish various types of changes would be useful in an evalua - tion of the criteria for determining what levels of authority are optimal for authorizing certain types of changes and for estimating future changes. Care must be taken to keep the focus of the surveillance on the insights that can be gained from the measurements, not on the measurements themselves. Discussion of software process and product measurement is presented in the Soft - ware Engineering Process KA. Software mea - surement programs are described in the Software Engineering Management KA. 1.5.2. In-Process Audits of SCM [3*, c1s1] Audits can be carried out during the software engineering process to investigate the current sta - tus of specific elements of the configuration or to assess the implementation of the SCM process. In-process auditing of SCM provides a more for - mal mechanism for monitoring selected aspects of the process and may be coordinated with the SQA function (see topic 5, Software Configura - tion Auditing). 2. Software Configuration Identification [2*, c8] [4*, c29s1.1] Software configuration identification identifies items to be controlled, establishes identification schemes for the items and their versions, and establishes the tools and techniques to be used in acquiring and managing controlled items. These activities provide the basis for the other SCM activities. 2.1. Identifying Items to Be Controlled [2*, c8s2.2] [4*, c29s1.1] One of the first steps in controlling change is identifying the software items to be controlled. This involves understanding the software config - uration within the context of the system configu - ration, selecting software configuration items, developing a strategy for labeling software items and describing their relationships, and identifying both the baselines to be used and the procedure for a baseline’s acquisition of the items. 2.1.1. Software Configuration [1, c3] Software configuration is the functional and phys - ical characteristics of hardware or software as set forth in technical documentation or achieved in a product. It can be viewed as part of an overall system configuration. 2.1.2. Software Configuration Item [4*, c29s1.1] A configuration item (CI) is an item or aggre - gation of hardware or software or both that is designed to be managed as a single entity. A soft - ware configuration item (SCI) is a software entity that has been established as a configuration item [1]. The SCM typically controls a variety of items in addition to the code itself. Software items with potential to become SCIs include plans, specifi - cations and design documentation, testing mate - rials, software tools, source and executable code, code libraries, data and data dictionaries, and documentation for installation, maintenance, operations, and software use. Selecting SCIs is an important process in which a balance must be achieved between pro - viding adequate visibility for project control pur - poses and providing a manageable number of controlled items. 2.1.3. Software Configuration Item Relationships [3*, c7s4] Structural relationships among the selected SCIs, and their constituent parts, affect other SCM activities or tasks, such as software building or analyzing the impact of proposed changes. Proper tracking of these relationships is also important for supporting traceability. The design of the identification scheme for SCIs hould consider the need to map identified items to the software structure, as well as the need to support the evolution of the software items and their relationships. 2.1.4. Software Version [1, c3] [4*, c29s3] Software items evolve as a software project pro - ceeds. A version of a software item is an identi - fied instance of an item. It can be thought of as a state of an evolving item. A variant is a version of a program resulting from the application of soft - ware diversity. 2.1.5. Baseline [1, c3] A software baseline is a formally approved ver - sion of a configuration item (regardless of media) that is formally designated and fixed at a specific time during the configuration item’s life cycle. The term is also used to refer to a particular ver - sion of a software configuration item that has been agreed on. In either case, the baseline can only be changed through formal change con - trol procedures. A baseline, together with all approved changes to the baseline, represents the current approved configuration. Commonly used baselines include func - tional, allocated, developmental, and product baselines. The functional baseline corresponds to the reviewed system requirements. The allo - cated baseline corresponds to the reviewed software requirements specification and soft - ware interface requirements specification. The developmental baseline represents the evolving software configuration at selected times during the software life cycle. Change authority for this baseline typically rests primarily with the development organization but may be shared with other organizations (for example, SCM or Test). The product baseline corresponds to the completed software product delivered for sys - tem integration. The baselines to be used for a given project, along with the associated levels of authority needed for change approval, are typi - cally identified in the SCMP. 2.1.6. Acquiring Software Configuration Items [3*, c18] Software configuration items are placed under SCM control at different times; that is, they are incorporated into a particular baseline at a particu - lar point in the software life cycle. The triggering event is the completion of some form of formal acceptance task, such as a formal review. Figure 6.2 characterizes the growth of baselined items as the life cycle proceeds. This figure is based on the waterfall model for purposes of illustration only; the subscripts used in the figure indicate versions 6-8 SWEBOK® Guide

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of the evolving items. The software change request (SCR) is described in section 3.1. In acquiring an SCI, its origin and initial integ - rity must be established. Following the acquisi - tion of an SCI, changes to the item must be for - mally approved as appropriate for the SCI and the baseline involved, as defined in the SCMP. Following approval, the item is incorporated into the software baseline according to the appropriate procedure. 2.2. Software Library [3*, c1s3] [4*, c29s1.2] A software library is a controlled collection of software and related documentation designed to aid in software development, use, or maintenance [1]. It is also instrumental in software release man - agement and delivery activities. Several types of libraries might be used, each corresponding to the software item’s particular level of maturity. For example, a working library could support coding and a project support library could support test - ing, while a master library could be used for fin - ished products. An appropriate level of SCM con - trol (associated baseline and level of authority for change) is associated with each library. Security, in terms of access control and the backup facili - ties, is a key aspect of library management. The tool(s) used for each library must support the SCM control needs for that library—both in terms of controlling SCIs and controlling access to the library. At the working library level, this is a code management capability serving develop - ers, maintainers, and SCM. It is focused on man - aging the versions of software items while sup - porting the activities of multiple developers. At higher levels of control, access is more restricted and SCM is the primary user. These libraries are also an important source of information for measurements of work and progress. 3. Software Configuration Control [2*, c9] [4*, c29s2] Software configuration control is concerned with managing changes during the software life cycle. It covers the process for determining what changes to make, the authority for approv - ing certain changes, support for the implementa - tion of those changes, and the concept of formal deviations from project requirements as well as waivers of them. Information derived from these activities is useful in measuring change traffic and breakage as well as aspects of rework. 3.1. Requesting, Evaluating, and Approving Software Changes [2*, c9s2.4] [4*, c29s2] The first step in managing changes to controlled items is determining what changes to make. The software change request process (see a typical flow of a change request process in Figure 6.3) provides formal procedures for submitting and recording change requests, evaluating the poten - tial cost and impact of a proposed change, and accepting, modifying, deferring, or rejecting the proposed change. A change request (CR) is a request to expand or reduce the project scope; modify policies, processes, plans, or procedures; modify costs or budgets; or revise schedules [1]. Requests for changes to software configura - tion items may be originated by anyone at any point in the software life cycle and may include a suggested solution and requested priority. One source of a CR is the initiation of corrective action in response to problem reports. Regardless of the source, the type of change (for example, defect or enhancement) is usually recorded on the Software CR (SCR). This provides an opportunity for tracking defects and collecting change activity measure - ments by change type. Once an SCR is received, a technical evaluation (also known as an impact analysis) is performed to determine the extent of the modifications that would be necessary should the change request be accepted. A good under - standing of the relationships among software (and, possibly, hardware) items is important for this task. Finally, an established authority—com - mensurate with the affected baseline, the SCI involved, and the nature of the change—will evaluate the technical and managerial aspects of the change request and either accept, modify, reject, or defer the proposed change. Software Configuration Management 6-9 3.1.1. Software Configuration Control Board [2*, c9s2.2] [3*, c11s1] [4*, c29s2] The authority for accepting or rejecting proposed changes rests with an entity typically known as a Configuration Control Board (CCB). In smaller projects, this authority may actually reside with the leader or an assigned individual rather than a multiperson board. There can be multiple levels of change authority depending on a variety of cri - teria—such as the criticality of the item involved, the nature of the change (for example, impact on budget and schedule), or the project’s current point in the life cycle. The composition of the CCBs used for a given system varies depending on these criteria (an SCM representative would always be present). All stakeholders, appropriate to the level of the CCB, are represented. When the scope of authority of a CCB is strictly soft - ware, it is known as a Software Configuration Control Board (SCCB). The activities of the CCB are typically subject to software quality audit or review. 3.1.2. Software Change Request Process [3*, c1s4, c8s4] An effective software change request (SCR) pro - cess requires the use of supporting tools and pro - cedures for originating change requests, enforc - ing the flow of the change process, capturing CCB decisions, and reporting change process information. A link between this tool capability and the problem-reporting system can facilitate the tracking of solutions for reported problems. 3.2. Implementing Software Changes [4*, c29] Approved SCRs are implemented using the defined software procedures in accordance with the applicable schedule requirements. Since a number of approved SCRs might be implemented simultaneously, it is necessary to provide a means for tracking which SCRs are incorporated into particular software versions and baselines. As part of the closure of the change process, com - pleted changes may undergo configuration audits and software quality verification—this includes ensuring that only approved changes have been made. The software change request process described above will typically document the SCM (and other) approval information for the change. Changes may be supported by source code ver - sion control tools. These tools allow a team of software engineers, or a single software engineer, to track and document changes to the source code. These tools provide a single repository for storing the source code, can prevent more than one soft - ware engineer from editing the same module at the same time, and record all changes made to the Figure 6.3. Flow of a Change Control Process 6-10 SWEBOK® Guide

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source code. Software engineers check modules out of the repository, make changes, document the changes, and then save the edited modules in the repository. If needed, changes can also be discarded, restoring a previous baseline. More powerful tools can support parallel development and geographically distributed environments. These tools may be manifested as separate, specialized applications under the control of an independent SCM group. They may also appear as an integrated part of the software engineering environment. Finally, they may be as elementary as a rudimentary change control system provided with an operating system. 3.3. Deviations and Waivers [1, c3] The constraints imposed on a software engineer - ing effort or the specifications produced during the development activities might contain provisions that cannot be satisfied at the designated point in the life cycle. A deviation is a written autho - rization, granted prior to the manufacture of an item, to depart from a particular performance or design requirement for a specific number of units or a specific period of time. A waiver is a writ - ten authorization to accept a configuration item or other designated item that is found, during produc - tion or after having been submitted for inspection, to depart from specified requirements but is nev - ertheless considered suitable for use as-is or after rework by an approved method. In these cases, a formal process is used for gaining approval for deviations from, or waivers of, the provisions. 4. Software Configuration Status Accounting [2*, c10] Software configuration status accounting (SCSA) is an element of configuration management con - sisting of the recording and reporting of informa - tion needed to manage a configuration effectively. 4.1. Software Configuration Status Information [2*, c10s2.1] The SCSA activity designs and operates a sys - tem for the capture and reporting of necessary information as the life cycle proceeds. As in any information system, the configuration status infor - mation to be managed for the evolving configura - tions must be identified, collected, and maintained. Various information and measurements are needed to support the SCM process and to meet the con - figuration status reporting needs of management, software engineering, and other related activities. The types of information available include the approved configuration identification as well as the identification and current implementation sta - tus of changes, deviations, and waivers. Some form of automated tool support is neces - sary to accomplish the SCSA data collection and reporting tasks; this could be a database capabil - ity, a stand-alone tool, or a capability of a larger, integrated tool environment. 4.2. Software Configuration Status Reporting [2*, c10s2.4] [3*, c1s5, c9s1, c17] Reported information can be used by various organizational and project elements—including the development team, the maintenance team, project management, and software quality activi - ties. Reporting can take the form of ad hoc que - ries to answer specific questions or the periodic production of predesigned reports. Some infor - mation produced by the status accounting activity during the course of the life cycle might become quality assurance records. In addition to reporting the current status of the configuration, the information obtained by the SCSA can serve as a basis of various measure - ments. Examples include the number of change requests per SCI and the average time needed to implement a change request. 5. Software Configuration Auditing [2*, c11] A software audit is an independent examina - tion of a work product or set of work products to assess compliance with specifications, standards, contractual agreements, or other criteria [1]. Audits are conducted according to a well-defined process consisting of various auditor roles and responsibilities. Consequently, each audit must be carefully planned. An audit can require a num - ber of individuals to perform a variety of tasks over a fairly short period of time. Tools to support Software Configuration Management 6-11 the planning and conduct of an audit can greatly facilitate the process. Software configuration auditing determines the extent to which an item satisfies the required functional and physical characteristics. Informal audits of this type can be conducted at key points in the life cycle. Two types of formal audits might be required by the governing contract (for exam - ple, in contracts covering critical software): the Functional Configuration Audit (FCA) and the Physical Configuration Audit (PCA). Successful completion of these audits can be a prerequisite for the establishment of the product baseline. 5.1. Software Functional Configuration Audit [2*, c11s2.1] The purpose of the software FCA is to ensure that the audited software item is consistent with its governing specifications. The output of the soft - ware verification and validation activities (see Verification and Validation in the Software Qual - ity KA) is a key input to this audit. 5.2. Software Physical Configuration Audit [2*, c11s2.2] The purpose of the software physical configura - tion audit (PCA) is to ensure that the design and reference documentation is consistent with the as-built software product. 5.3. In-Process Audits of a Software Baseline [2*, c11s2.3] As mentioned above, audits can be carried out during the development process to investigate the current status of specific elements of the con - figuration. In this case, an audit could be applied to sampled baseline items to ensure that per - formance is consistent with specifications or to ensure that evolving documentation continues to be consistent with the developing baseline item. 6. Software Release Management and Delivery [2*, c14] [3*, c8s2] In this context, release refers to the distribu - tion of a software configuration item outside the development activity; this includes internal releases as well as distribution to customers. When different versions of a software item are available for delivery (such as versions for different plat - forms or versions with varying capabilities), it is frequently necessary to recreate specific versions and package the correct materials for delivery of the version. The software library is a key element in accomplishing release and delivery tasks. 6.1. Software Building [4*, c29s4] Software building is the activity of combining the correct versions of software configuration items, using the appropriate configuration data, into an executable program for delivery to a customer or other recipient, such as the testing activity. For systems with hardware or firmware, the executable program is delivered to the system-building activ - ity. Build instructions ensure that the proper build steps are taken in the correct sequence. In addition to building software for new releases, it is usually also necessary for SCM to have the capability to reproduce previous releases for recovery, testing, maintenance, or additional release purposes. Software is built using particular versions of supporting tools, such as compilers (see Com - piler Basics in the Computing Foundations KA). It might be necessary to rebuild an exact copy of a previously built software configuration item. In this case, supporting tools and associated build instructions need to be under SCM control to ensure availability of the correct versions of the tools. A tool capability is useful for selecting the cor - rect versions of software items for a given target environment and for automating the process of building the software from the selected versions and appropriate configuration data. For projects with parallel or distributed development envi - ronments, this tool capability is necessary. Most software engineering environments provide this capability. These tools vary in complexity from requiring the software engineer to learn a spe - cialized scripting language to graphics-oriented approaches that hide much of the complexity of an “intelligent” build facility. The build process and products are often sub - ject to software quality verification. Outputs of 6-12 SWEBOK® Guide

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the build process might be needed for future refer - ence and may become quality assurance records. 6.2. Software Release Management [4*, c29s3.2] Software release management encompasses the identification, packaging, and delivery of the elements of a product—for example, an execut - able program, documentation, release notes, and configuration data. Given that product changes can occur on a continuing basis, one concern for release management is determining when to issue a release. The severity of the problems addressed by the release and measurements of the fault den - sities of prior releases affect this decision. The packaging task must identify which product items are to be delivered and then select the correct variants of those items, given the intended appli - cation of the product. The information document - ing the physical contents of a release is known as a version description document .

The release 

notes typically describe new capabilities, known problems, and platform requirements necessary for proper product operation. The package to be released also contains installation or upgrading instructions. The latter can be complicated by the fact that some current users might have versions that are several releases old. In some cases, release management might be required in order to track distribution of the product to various customers or target systems—for example, in a case where the supplier was required to notify a customer of newly reported problems. Finally, a mechanism to ensure the integrity of the released item can be implemented—for example by releasing a digital signature with it.

A tool capability is needed for supporting 

these release management functions. It is use - ful to have a connection with the tool capability supporting the change request process in order to map release contents to the SCRs that have been received. This tool capability might also maintain information on various target platforms and on various customer environments. 7. Software Configuration Management Tools [3*, c26s1] [4*, c8s2] When discussing software configuration manage - ment tools, it is helpful to classify them. SCM tools can be divided into three classes in terms of the scope at which they provide support: indi - vidual support, project-related support, and com - panywide-process support. Individual support tools

are appropriate and 

typically sufficient for small organizations or development groups without variants of their software products or other complex SCM require - ments. They include: • Version control tools: track, document, and store individual configuration items such as source code and external documentation. • Build handling tools: in their simplest form, such tools compile and link an executable version of the software. More advanced building tools extract the latest version from the version control software, perform qual - ity checks, run regression tests, and produce various forms of reports, among other tasks. • Change control tools: mainly support the control of change requests and events noti - fication (for example, change request status changes, milestones reached). Project-related support tools

mainly support 

workspace management for development teams and integrators; they are typically able to sup - port distributed development environments. Such tools are appropriate for medium to large organi - zations with variants of their software products and parallel development but no certification requirements. Companywide-process support tools

can typi

- cally automate portions of a companywide pro - cess, providing support for workflow manage - ments, roles, and responsibilities. They are able to handle many items, data, and life cycles. Such tools add to project-related support by supporting a more formal development process, including certification requirements. Software Configuration Management 6-15 FURTHER READINGS Stephen P. Berczuk and Brad Appleton, Software Configuration Management Patterns: Effective Teamwork, Practical Integration

[6].

This book expresses useful SCM practices and strategies as patterns. The patterns can be imple - mented using various tools, but they are expressed in a tool-agnostic fashion. “CMMI for Development,” Version 1.3, pp. 137–147 [7]. This model presents a collection of best prac - tices to help software development organizations improve their processes. At maturity level 2, it suggests configuration management activities. REFERENCES [1] ISO/IEC/IEEE 24765:2010 Systems and Software Engineering—Vocabulary , ISO/ IEC/IEEE, 2010. [2*] IEEE Std. 828-2012, Standard for Configuration Management in Systems and Software Engineering , IEEE, 2012. [3*] A.M.J. Hass, Configuration Management Principles and Practices , 1st ed., Addison- Wesley, 2003. [4*] I. Sommerville, Software Engineering , 9th ed., Addison-Wesley, 2011. [5*] J.W. Moore, The Road Map to Software Engineering: A Standards-Based Guide , Wiley-IEEE Computer Society Press, 2006. [6] S.P. Berczuk and B. Appleton, Software Configuration Management Patterns: Effective Teamwork, Practical Integration , Addison-Wesley Professional, 2003. [7] CMMI Product Team, “CMMI for Development, Version 1.3,” Software Engineering Institute, 2010; http:// resources.sei.cmu.edu/library/asset-view. cfm?assetID=9661