Requirements Management
Lead Author: Tami Katz Contributing Authors: Lou Wheatcraft, Mike Ryan
Requirements management is performed to ensure alignment of the system requirements with other representations, analyses, and artifacts of the system. It includes providing an understanding of the requirements, establishing a baseline, communicating the requirements, managing changes, providing status of the requirement and associated verification process, and maintaining traceability among the requirements and with the rest of the artifacts of system definition.
Purpose and Definition
Requirements Management is the discipline of gathering, expressing, organizing, tracing, analyzing, reviewing, agreeing, tracking, communicating, changing and validating requirement statements (Pohl, 2010). While requirements develop addresses elicitation and creation of the requirements as described in System Requirements Definition, the requirements management process addresses how the products of that activity are managed over the project life cycle. This process leverages the other systems engineering management processes of Configuration Management and Information Management in addressing the activities highlighted in Figure 1.
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Figure 1. Requirements Management Activities. This figure is derived from the INCOSE Guide to Needs and Requirements v1, Figure 22, reprinted with permission of INCOSE. All other rights are reserved by the copyright owner.
The scope of requirements management also includes management of artifacts from the System Concept Definition activities Business or Mission Analysis and Stakeholder Needs Definition, as well as traceability of requirements to other systems engineering artifacts as described in System Requirements Definition.
Process Approach
Requirements management begins with the definition of stakeholder needs and system requirements, ensuring the data from these activities are captured, configuration controlled, and communicated. Enablers for requirements management include attributes, tools, and configuration management processes.
Configuration Management and Change Control
Requirements management is also closely tied to configuration management for baseline management and control. When the requirements have been defined, assessed, and approved, they are baselined. The baseline allows the project to analyze and understand the impact (technical, cost, and schedule) of any proposed changes. There are several reasons requirements could change, including
- Continuing maturity through resolution of TBXs
- Re-allocation of system performance
- Changing operational environments
- Changing external interfaces
- Introduction of new technology and Innovation
- Obsolescence
- Customer budget changes
- Regulation changes
- Changes in the market
- Emerging threats and risks
Requirement changes can include modifications, new requirements or deleted requirements. Once a requirement is baselined, changes must come with rationale to explain to the stakeholders why this change is occurring, which helps with assessment of impact. Impacts could include the cost of making requirement changes at multiple levels in the architecture hierarchy, including suppliers, as well as the cost/schedule/technical impacts associated with any work-in-process updates (design, verification planning, verification execution, etc.). Impacts to related requirements and interfaces also need to be considered when making changes to requirements. Traceability, described below, is a powerful enabler to support assessment and impact of requirement changes.
Monitoring and Control
The monitoring process uses the Measurement process to enable situational awareness of the status and quality of the requirement process, including status of requirement development completion, incorporation of changes, and progress towards obtaining objective evidence during System Verification. Controlling the requirements is actions taken to ensure requirements continue to address the stakeholder needs; this includes resolving unknowns, addressing findings in the quality and correctness of the requirements, and making changes.
Example metrics:
- Requirements quantity
- Requirements quality
- Requirements volatility (rate of change)
- Types of requirements
- Requirements not traceable to Stakeholder needs
- TBX Count (maturity)
- Completeness of system verification planning
This activity often supported through the use of attributes that provide additional content for the requirement. Example attributes to support requirements management include Status, Prioritization, Stability, and Responsible Person or Owner. A more complete list of attributes, their descriptions, and guidance for use is included in the INCOSE Needs and Requirements Manual (NRM).
Requirement Management Tools
There are many tools available to provide a supporting infrastructure for requirements management; the best choice is the one that matches the processes of the project or enterprise.
Desired capabilities and features of needs and requirements management tools include definition, collaboration, change control, and trace to other project data. A requirements management tool can enable a project's success with its execution and validation of end product through ability to:
- Capture requirements and associated attributes
- Capture requirement trace
- Generation of requirements metrics and status
- Manage version and changes of the requirements
- Facilitate change impact analysis
- Control access to edit/change requirements
- Enable reuse of requirements
Modern requirement management tools vary in capabilities and costs. Various capabilities and features to consider when choosing a tool is included in the INCOSE Needs and Requirements Manual (NRM).
Examples of different requirement management tools can be found in the INCOSE Systems Engineering Tools Database [link]. A list of various requirement management tools that have been rated by users can be found at https://www.g2.com/categories/requirements-management.
It is recommended that requirement management tools are connected to other project tools sets as part of a larger digital engineering ecosystem, as highlighted in Figure 2, to maximize the ability to trace to other project data.
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Figure 2. Requirement Management Tool as part of a Project's Digital Ecosystem. This figure is derived from the INCOSE Needs and Requirements Manual v1.1, Figure 16-1, reprinted with permission of INCOSE. All other rights are reserved by the copyright owner. Requirement management tools are most effective if they are setup with project configuration and templates before project usage, ensuring the project team spends their time on the definition and management of requirements and not on extensive development of the tool infrastructure.
Managing Traceability
As described in System Requirements Definition, during the development of requirements trace can be established between the requirements and other sets of data, including:
- Use Cases, operations they support
- Stakeholder Needs
- Higher-level requirements
- Lower-level requirements
- Other requirements with relationships (such as shared performance budgets from an allocation)
- Allocated products which satisfy the requirements
- Requirement rationale artifacts (reports, heritage)
- Evidence of verification (tests, records)
- Project data (budget, schedule, risks)
- Interface definitions
- Required standards and regulations
- Supplementary data
Requirements Management processes are used to monitor these traces and ensure they are maintained over the development life cycle. This is enabled through use of toolsets that allow linkages of the requirements to the other data within a digital ecosystem, as described above.
Requirements Management Planning
The processes of requirements management involve project resources and must be planned as part of the overall project and systems engineering planning efforts. A Requirements Management Plan (RMP) can be used to define and communicate scope and processes for managing requirements during the project lifecycle. Generating a RMP keeps all team members and stakeholders on the same page. For simple efforts, the RMP could be captured within the program management plan or systems engineering management plan.
Some of the key questions answered in a RMP include:
- Who will be responsible for requirements management activities?
- How will stakeholder requirements be identified?
- How will requirement quality and validation be accomplished?
- How will requirements be prioritized?
- What types of traceability will be used?
- What is the specification tree and how will it be managed?
- What attributes will be used?
- How will status be measured?
- How are TBX managed?
- How will changes be managed?
- What is the process for allocation and budgeting of requirements?
- What tool(s) will be used?
Plan for the requirements management approach based on the scale and complexity of the effort and generate a RMP accordingly, and then update the plan if the processes evolve. Note that some projects are required to deliver their plan to a customer, which may require additional content; however, do not generate a plan merely because a customer directed it. Proper planning can ensure desired outcomes when implementing a requirements management process.
References
Works Cited
INCOSE. 2022. INCOSE Needs and Requirements Manual, version 1.1. INCOSE-TP-2021-002-01.
INCOSE. 2022. INCOSE Guide to Needs and Requirements, version 1. INCOSE-TP-2021-003-01.
Pohl, K. (2010). Requirements Engineering Fundamentals, Principles, and Techniques.
Primary References
INCOSE. 2022. INCOSE Needs and Requirements Manual, version 1.1. INCOSE-TP-2021-002-01.
INCOSE. 2022. INCOSE Guide to Needs and Requirements, version 1. INCOSE-TP-2021-003-01.
Additional References
Katz, T. 2021. Cost Optimization in Requirements Management for Space Systems. PhD Dissertation, Dept. of Systems Engineering, Colorado State University.
Video References
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