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- 1. The Requirement
- 2. Rationale
- 3. Guidance
- 4. Small Projects
- 5. Resources
- 6. Lessons Learned
- 7. Software Assurance
1. Requirements
5.4.6 The project manager shall collect, track, and report software requirements volatility metrics.
1.1 Notes
NPR 7150.2, NASA Software Engineering Requirements, does not include any notes for this requirement.
1.2 History
1.3 Applicability Across Classes
Class A B C D E F Applicable?
Key: - Applicable | - Not Applicable
2. Rationale
Requirements volatility is one of the leading causes of the software development effort not completing on schedule and budget. Software requirements volatility is one key factor in assessing the status of a software project. The later in the project requirements changes occur, the more impact those changes can have on project completion on time and within budget.
3. Guidance
3.1 Applicability
This requirement applies to all NASA centers for Class A and B software. Class C software development efforts may also consider collecting these metrics, especially if the development schedule is very tight. See also Topic 5.01 - CR-PR - Software Change Request - Problem Report,
3.2 Impact Of Requirements Changes
Requirements changes can occur throughout the entire lifecycle. Requirements changes for clarification or to add something that was overlooked are usually caught fairly early on in the lifecycle. In general, by PDR most requirements have been identified and refined. The cost of these changes, before PDR, is anticipated in the overall cost of the project.
3.3 Tracking Requirements Volatility
It is important to keep track of requirements changes, especially later in the development lifecycle, so that an assessment can be made of the impact of these changes on the overall project cost and schedule. This assessment allows the project manager to make better-informed decisions on the implementation of the changes. Tracking requirements volatility over time can help identify potential process improvements that need to be made to enhance efficiency and productivity in the future.
3.4 Reporting Requirements Volatility Metrics
Requirements volatility metrics are reported to the project manager and others regularly. They are also reported to the Software Engineering Process Group (SEPG) to help with future project cost estimation.
Some metrics to consider are:
- Monitor and control changes in the software scope.
- Number of requirements
- Number of requirements changes
- Number of TBR/TBDs over time
- Assess the extent and cost of product rework.
- Rework trend over time
- Cost of the rework
See also SWE-094 - Reporting of Measurement Analysis.
3.5 Additional Guidance
Additional guidance related to this requirement may be found in the following materials in this Handbook:
Related Links |
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3.6 Center Process Asset Libraries
SPAN - Software Processes Across NASA
SPAN contains links to Center managed Process Asset Libraries. Consult these Process Asset Libraries (PALs) for Center-specific guidance including processes, forms, checklists, training, and templates related to Software Development. See SPAN in the Software Engineering Community of NEN. Available to NASA only. https://nen.nasa.gov/web/software/wiki 197
See the following link(s) in SPAN for process assets from contributing Centers (NASA Only).
SPAN Links |
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4. Small Projects
No additional guidance is available for small projects.
5. Resources
5.1 References
- (SWEREF-197) Software Processes Across NASA (SPAN) web site in NEN SPAN is a compendium of Processes, Procedures, Job Aids, Examples and other recommended best practices.
5.2 Tools
NASA users find this in the Tools Library in the Software Processes Across NASA (SPAN) site of the Software Engineering Community in NEN.
The list is informational only and does not represent an “approved tool list”, nor does it represent an endorsement of any particular tool. The purpose is to provide examples of tools being used across the Agency and to help projects and centers decide what tools to consider.
6. Lessons Learned
6.1 NASA Lessons Learned
No Lessons Learned have currently been identified for this requirement.
6.2 Other Lessons Learned
No other Lessons Learned have currently been identified for this requirement.
7. Software Assurance
7.1 Tasking for Software Assurance
1. Confirm that the project collects, tracks, and reports on the software volatility metrics.
7.2 Software Assurance Products.
- SA analysis of software volatility measures over time.
Objective Evidence
- Software measurement or metric data showing software volatility
- Trends and analysis results on the metric set being provided
- Status presentation showing metrics and treading data
7.3 Metrics
- Software Requirements Volatility (# of requirements added, deleted, modified, # of TBDs over time)
Note: Metrics in bold type are required for all projects
See also Topic 8.18 - SA Suggested Metrics.
7.4 Guidance
Requirements volatility is the change in requirements (added, deleted, and modified) over a given time interval. The success of software projects is dependent on the quality of requirements, especially given that requirements are the basis for planning project schedules as well as design and test specifications.
Examples:
Software requirements volatility is expected during the early stages of a project (conceptualize / requirements phase). It becomes a concern when it occurs after the software requirements phase (after CDR) is complete because it is likely to result in the re-work of the software components.
Even though there are good requirements, in the beginning, the software requirements may be changed during the project development. Software requirement changes during the software development process are also known as Requirements Volatility.
Requirements volatility has a great impact on the cost, the schedule, and the quality of the final product. Due to requirements volatility, many projects fail and some are completed partially. Requirements volatility cannot be overcome fully but we can minimize it with some requirement measures or metrics. Requirement metrics are useful in identifying the risks of a project by locating errors in the requirements document.
Requirements evolution is due to factors.
- External Factors:
- Government regulations
- project direction and changes
- project funding
- Internal factors
- Hardware and interface constraints and unknowns
- Lack of experience in the system requirements and software requirements development team
- Feedback from milestone reviews and peer reviews
- Complexity
- Customer, operational, software, and hardware changes
- Hazard identifications
- Lack of process maturity in requirements generation and requirements management
- Requirement or hardware reuse
- Environmental changes or mission profile changes
- Requirements instability (the extent of fluctuation in user requirements)
- Requirements diversity (the extent to which stakeholders disagree among themselves deciding on requirements).
- Requirements analyzability (the extent to which the process of producing requirement -specification can be reduced to objective procedure).
- Poor communication between users and the development team.
Requirements volatility contains schedule, cost, and performance risk factors. Developing and maintaining a trending of software requirements volatility measurements is critical to determine the risks associated with the project.
Requirement volatility is not the only reason contributing to the success of any project, by can be a key indicator of the project risk and success.
Several challenges lead to Requirement Volatility.
- The change request form was not always complete. A change request form may have little information about the reason for the proposed change.
- No formal impact analysis and incomplete change effort estimation.
- Traceability between requirements and other software artifacts is not established. See SWE-052 - Bidirectional Traceability
The impact of requirement volatility on the software project has been seen as:
- Projects Schedule: If the schedule of one activity is delayed, obviously all subsequent activities schedule will be disturbed.
- Project Performance: Project performance decreases due to the changes in requirements. Requirement Volatility has a high impact on the coding and maintenance phases.
- Project Cost: Project cost increases due to a change in requirements.
- S/W Maintenance
- S/W Quality: The quality of software decreases due to continuous changes in requirements.
Though requirements volatility has an impact on the project schedule, project performance, project cost, software maintenance, and software quality, it may have some positive effects as well as may help us to have a better understanding of user requirements.
7.5 Additional Guidance
Additional guidance related to this requirement may be found in the following materials in this Handbook:
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