Configuration control procedures are important because they help ensure that arbitrary changes are avoided and that the team understands how changes are to be managed for the project.
The configuration management (CM) plan documents the configuration control and change authorization procedures (see SWE-079 and SCMP). When developing these procedures, all of the following topics are included: levels of control, change authority, authorization requests, change request process, and version maintenance. The STEP Level 2 Software Configuration Management and Data Management course taught by the Westfall Team includes recommendations and suggestions for change control, some of which is summarized in this guidance.
Levels of control
Each identified configuration item (CI) has a defined level of control for making changes to that item. Documentation might have one level of change control, while source code might require a different level of control. For each identified CI or group/class of items, the change control procedures identify the appropriate level of control. Consider the following when defining levels of configuration control:
- Each CI or class of items has a defined "owner" who is responsible for authorizing changes to that item, e.g., the software Change Control Board (CCB) might be the designated owner for all software libraries while the documentation peer review team might be the owner for product marketing materials.
- Depending on the effect of the change, multiple levels of control may need to be defined, e.g., a change to software that is shared among projects may require change approval from multiple change authorities.
- Levels of control may vary throughout the life cycle, e.g., changes to code in development may require a lower level of control than changes to the same code after it has been released.
- Levels of control may be affected by the change originator, e.g., a change request from outside the organization, such as customers or end users, may require different authority for approval than changes requested by software developers.
Change control procedures include defining the persons or groups with authority to authorize changes and to make changes at each level. Examples of change authority include CCBs, Change Authorization Board (CAB), Engineering Change Boards (ECBs), peer review teams, project manager, etc. The change approval authority may be determined by the complexity, cost, risk, or effect of the change. When defining the change authority, consider the following:
- Include software assurance/safety personnel to ensure safety impact is considered.
- Involve stakeholders based on the expertise and authority required to disposition the change.
- People with authority in the appropriate fields.
- Experts in a particular field.
- Policy makers.
- Systems engineers.
- Software engineers.
- Hardware engineers.
- Use different levels of change authority, as appropriate, for cost and time savings.
- Product level CCB for changes to functional baseline, product baseline, system-level changes or changes that will affect the fielded product.
- Project level CCB for changes to allocated baselines, changes that only affect the project, not the system.
- Software development CCB for changes to development baselines, changes that only affect the software, not hardware or documentation.
- If different levels of authority are used:
- Group size can be less at the lower levels.
- Typically one representative from the lower level sits on the next level CAB.
- Escalation can occur if a lower level change authority cannot agree on disposition of a change.
- An escalation plan is typically defined as part of the change control procedures.
- Coordination plans may be required if multiple change authorities are required to disposition a change.
- Typically costs more in time and effort to convene higher level change authority boards, so they tend to meet less frequently.
- Document the responsibilities of each level of authority, including, as applicable:
- Area of change authority, such as software changes, system-level changes, documentation changes, etc.
- Review and disposition of change requests.
- Authorizing release and delivery of baselined software products.
- Documenting and retaining evidence of the group's authorization activities.
- Informing the appropriate stakeholders of the results of those authorization activities.
Change control procedures include steps to be followed to request authorization for changes. Consider the following when documenting the steps to request authorization for making a change:
- Include instructions for choosing the proper change request to submit (Engineering Change Proposal (ECP), change request (CR), problem report (PR), etc. as appropriate and applicable for the project).
- Include instructions for properly completing the change request, typically a form in an automated change control system (see CR-PR for recommended change request contents), such that the change authority can make an informed disposition decision.
- Include instructions for supplying information not captured in the change request, but necessary for the change authority to disposition the request.
- Include instructions for determining the proper change authority.
- Include instructions for submitting a request to the proper change authority.
- Include information regarding when the change originator expects to receive the disposition decision from the change authority.
Change request process
The change request process consists of three steps described in the change control procedures: Change request processing, tracking changes, and distributing changes.
When developing procedures for processing change requests, consider:
- Using a screener to ensure the changes requests are properly completed and have been checked for technical correctness before higher level CABs spends time on incomplete or out-of-scope requests (see CR-PR for change request contents).
- Giving the change authority board the ability to perform impact analysis (see SWE-080) themselves or to call on another group with greater specific expertise to do the analysis.
- Describing the disposition options (once the analysis is complete, the change authority dispositions the change request, typically, in one of three ways: Approve for implementation, defer the change until some later point in time, or reject the change request).
- Requiring the basis for the disposition to be documented and the disposition disseminated to the appropriate stakeholders.
A sample process flow might look like this chart adapted from the STEP Level 2 Software Configuration Management and Data Management course:
When developing procedures for tracking changes, consider:
- Collecting status as the change request is processed (open, fixed, resolved, closed, etc.) along with the status change dates.
- Capturing the impact analysis for each change.
- Collecting disposition status (approved, deferred, rejected) and date.
- Capturing the solution implemented for each change.
- Capturing the verification activity and results for each implemented change.
- Capturing all CIs affected by the change (requirements, design, tests, source code, documentation, etc.).
- Using the features of CM tools to track changes and related metrics and data.
- Tracking changes to all identified CIs (see SWE-081).
- Reporting status of changes to project management on a regular basis; reporting frequency may be established based on the life-cycle phase of the project with documentation in the CM plan.
- Guidance provided in SWE-080 in this Handbook for tracking and evaluating changes.
When developing procedures for distributing changes, consider:
- Releasing changes only after verification and approval of their implementation.
- Releasing changes in a controlled manner, typically as part of a baseline (during development), patch or update (for changes to fielded software), or new fielded release.
- Using a software version description (SVD) or version description document (VDD) to identify the changes included in a software release.
When developing procedures for maintaining past versions of the software, consider:
- The ease of retrieving past versions to address issues found in fielded software.
- Tracking all released software that uses a particular version of a CI so that changes can be made to all affected software, not just the version for which the change was requested.
- Using features of CM tools, such as "tagging," to identify all items and their versions in a baseline or release.
When establishing change authority, consider coordinating or applying the same concepts as part of data management activities. A basic description of data management is provided in SWE-079.
NASA users should consult Center Process Asset Libraries (PALs) for Center-specific guidance and resources related to configuration control and authorizing changes.
NASA-specific change control information and resources are available in Software Processes Across NASA (SPAN), accessible to NASA users from the SPAN tab in this Handbook.
Additional guidance related to authorizing changes may be found in the following related requirements in this Handbook: