Incremental Development Approach
Lead Authors: David Endler Contributing Authors: Mike Yokell, Garry Roedler
Incremental development approaches offer a flexible and adaptive method suited for projects with high uncertainty or evolving requirements. Unlike sequential models, incremental development delivers value in chunks by breaking down the system into manageable increments, each providing a subset of capabilities. This allows for potential early deployment, faster feedback, and continuous improvement based on real-world insights. The article explores practical applications, planning challenges, and the importance of balancing a structured roadmap with flexibility. It also highlights the Incremental Commitment Spiral Model (ICSM), which integrates concurrent development and risk assessment to guide informed decisions across successive development cycles.
Concepts
Incremental development is a fundamental approach in systems engineering where a system evolves through repeated cycles (iterations) of planning, designing, implementing, and evaluating. Unlike sequential approaches, such as the Waterfall model, incremental development approaches allow for continuous refinement of both requirements and solutions based on feedback and learning obtained during each iteration.
The roots of incremental development can be traced back to the 1950s and 60s with early software and systems engineering projects that required more flexibility than rigid linear models could provide. Notably, Barry Boehm's Spiral Model in the 1980s formalized incremental development by emphasizing risk management and incremental progress. It later influenced many agile and incremental development methodologies used today.
When using an incremental approach, not every iteration results in a tangible increment (i.e., a deliverable or prototype). Some iterations serve primarily as learning opportunities -exploring technical feasibility, user needs, or integration challenges. These learning-focused cycles are crucial for reducing uncertainty and guiding future design decisions.
Iterations that do produce increments provide stakeholders with early, partial versions of the system. These early deliverables enable verification, validation, and feedback well before the final system is complete. This responsiveness to change and focus on incremental value helps ensure the system better meets user needs and environmental constraints.
Incremental development approaches are especially useful in complex, high-uncertainty projects such as those involving new technologies, evolving requirements, or significant stakeholder interaction. It supports a more adaptive planning process, enabling engineers to respond to change and reduce risks over time.
By embracing early feedback, learning, and flexibility, incremental development approaches help create more robust, user-centered systems. It aligns engineering efforts with real-world complexities, making it a powerful strategy for certain development environments.
Practical considerations
The incremental development approach typically determines user needs, defines requirements, then divides the remaining development into a series or sequence of iterations, some of which result in a tangible increment and some of which serve for learning.
Early iterations may focus more on exploration (modeling, simulation, or proof-of-concept studies) to reduce technical uncertainty or evaluate design alternatives. Systems engineers must be comfortable with partial or evolving system architectures, often working with incomplete data or preliminary interfaces.
Traceability and configuration management also take on a different character compared to a sequential development approach. Since requirements, design elements, and interfaces may evolve over several iterations, robust version control and clear documentation of assumptions and decisions become essential to prevent confusion or rework later.
Collaboration and communication are especially critical. Incremental development often involves frequent interactions with stakeholders, users, and other engineering disciplines. Systems engineers must facilitate this exchange, using tools like prototypes, models, or incremental demonstrations to ensure alignment across the team and with the project goals.
Validation and verification activities are also distributed more evenly across the project timeline. Rather than being concentrated at the end, these activities are planned into iterations, allowing for early detection of issues. This demands more flexible test planning and a willingness to revise test cases as the system evolves.
Proper planning of the increments is critical and at the same time challenging. On the one hand, stakeholders are expecting a “master plan” for the increments and on the other hand, subsequent increments build on the learnings from the previous increments.
Finally, engineers must be prepared to continuously reassess risks and priorities at each iteration boundary. Trade studies, system impact assessments, and integration planning become recurring tasks, helping to maintain system coherence and feasibility across changing project conditions.
An incremental development approach can also be used when it is critical to hit the market with a product at a certain point in time. In this case, it can be advantageous to bring a product with limited capabilities to the market to get “a foot in the door”. Successive increments follow to close the capability gaps.
Example development approach
Boehm’s Incremental Commitment Spiral Model (ICSM) shown in Figure 1 is a modern incremental approach which extends the classic Spiral Model (Boehm, 1987) for software introduced by Boehm for SE. It is designed to address the challenges of complex, high-risk systems engineering projects. It combines the strengths of traditional, plan-driven methods with the flexibility of iterative and agile practices, offering a structured way to deliver systems in well-defined increments while continuously managing uncertainty and stakeholder alignment.
In ICSM, system development is divided into a series of incremental cycles, each leading to a decision point, or commitment review. Rather than committing to a full system design early on, stakeholders and engineers make incremental commitments only as far as the evidence and confidence gathered in each cycle justify. This allows projects to pivot, refine goals, or even stop development early if feasibility or value cannot be demonstrated.
Each cycle involves activities such as stakeholder engagement, feasibility assessments, risk analysis, and prototype development. If the results are promising, the project moves forward to the next increment, where additional capability is developed and validated. Over time, the system grows in maturity and functionality, reducing risk at each stage.
Unlike purely iterative models, ICSM provides clear decision checkpoints and is especially useful in projects requiring formal reviews, traceability, and accountability such as in defense, transportation, or critical infrastructure systems. It accommodates evolving requirements while maintaining a disciplined engineering process.
For systems engineers, working with ICSM means managing incremental baselines, tracking decisions across cycles, and facilitating informed stakeholder commitments. The model encourages early and continuous validation, with learning cycles embedded throughout the project.
References
Works Cited
INCOSE. 2023. "Chapter 2.2.2" in Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities, 5th Edition. Ed(s): D. Walden, T.M. Shortell, G.J. Roedler, B.A. Delicado, O. Mornas, Y. Yew-Seng, D. Endler. San Diego, CA: International Council on Systems Engineering (INCOSE). Available at https://www.incose.org/publications/se-handbook-v5.
Boehm, B. (1987). A spiral model of software development and enhancement, ACM SIGSOFT Software Engineering Notes, 11(4), 14–24.
Boehm, B., Lane, J., Koolmanojwong, S., and Turner, R. (2014). The Incremental Commitment Spiral Model: Principles and Practices for Successful Systems and Software, Addison‐Wesley Professional.
ISO/IEC/IEEE 24748-1. 2024. Systems and software engineering — Life cycle management, Part 1: Guidelines for life cycle management. Geneva, Switzerland: International Organization for Standardization (ISO), International Electrotechnical Commission, and Institute of Electrical and Electronics Engineers. Available at https://www.iso.org/standard/84709.html.
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