Foundations of Systems Engineering

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Lead Author: Rick Adcock, Contributing Authors: Scott Jackson, Janet Singer, Duane Hybertson, Gary Smith

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Part 2 of the SEBoK provides the conceptual foundations of systems engineering. It equips systems engineers with an understanding of the principles, theories, and practices that underpin their discipline, while also connecting them to the broader traditions of systems science and systems practice. By presenting this wider integrative context, Part 2 makes systems knowledge more accessible both within engineering and to a wider community of practitioners and researchers working across diverse domains.

Figure 1. SEBoK Part 2 in context (SEBoK Original). For more detail seeStructure of the SEBoK

This knowledge is included in the SEBoK firstly to help systems engineers benefit from an understanding of the foundations of their discipline, and to provide them with access to some of the theories and practices of systems science and other fields of systems practice. Including this wider integrative systems science context in the SEBoK should also help to make SE knowledge more accessible to a wider audience outside of its traditional domains.

Knowledge Areas in Part 2

Each part of the SEBoK is divided into knowledge areas (KAs), which are groupings of information with a related theme. Part 2 contains the following KAs:

• Systems Fundamentals introduces essential definitions, concepts, principles, and heuristics that underpin all of SE.
• The Nature of Systems explores the diversity of systems in the world, from natural and engineered to socio-technical, and the universal patterns they share.
• Systems Science surveys theoretical advances and enduring insights that support systemic understanding across domains.
• Systems Thinking describes the perspectives, principles, and heuristics that guide how we frame and approach complex problems.
• Representing Systems with Models highlights the role of abstraction and modeling in understanding, designing, and managing systems.
• Systems Approach Applied to Engineered Systems presents structured methods for applying systems concepts directly to real-world engineering practice

Introduction

Most systems engineers are practitioners, applying processes and methods that have been developed and evolved over decades. SE is a pragmatic approach, inherently interdisciplinary, yet specialized in its focus on integration and whole-system effectiveness. Practitioners typically work within a specific domain, using approaches tailored to that domain’s problems, constraints, risks, and opportunities. These approaches capture the accumulated knowledge of domain experts regarding the most effective ways to apply systems engineering.

Specific domains in which systems approaches are used and adapted include:

• Technology products, integrating multiple engineering disciplines
• Information-rich systems, such as command and control, air traffic management, or health informatics.
• Platforms, e.g. aircraft, civil airliners, cars, trains, etc.
• Organizational and enterprise systems, which may be focused on delivering service or capability
• Civil engineering/infrastructure systems, e.g. roads networks, bridges, builds, communications networks, etc.

Each domain involves different kinds of systems and requires different skill sets. Yet across this diversity, there are underlying unifying systems principles that can enhance the effectiveness of systems approaches in any domain. In particular, shared knowledge of systems principles and terminology improves communication and enables systems engineers to integrate complex systems that span traditional domain boundaries (Sillitto 2012). This integrated approach is increasingly needed to solve today’s complex system challenges, but as these different communities come together, they may find that assumptions underpinning their worldviews are not shared.

General Systems Engineering Foundations

To bridge the gap between different domains and communities of practice, it is essential to establish the intellectual foundations of systems engineering and a common language for describing its key concepts and paradigms. An integrated systems approach to complex problems must combine elements of systems theories with practical methods. This ranges from the technical-systems focus that has traditionally dominated engineering to the learning-systems focus used in social and organizational interventions. A shared framework and terminology allow communities with diverse worldviews and skills to collaborate effectively toward common goals.

The SEBoK provides principles and concepts that can support all potential applications of systems engineering, while remaining adaptable to particular contexts. Much of the published knowledge in systems engineering originates from specific domains, such as defense, transportation, health, or enterprise systems, or from particular business models and technology areas. In the SEBoK, this specialized knowledge is generalized where possible, so that it can be applied across related applications.

Generalized knowledge may take different forms. In many cases, it is informal generalization, representing current best understanding across domains or capturing common practices. In other cases, it is based on stronger theoretical considerations, offering explanatory power and predictive value across all special cases. SEBoK typically presents the informally generalized view, while identifying and linking specific knowledge to its broader foundations.

Looking ahead, the INCOSE Vision 2035 highlights the aspiration for systems engineering to mature into a discipline with a formally defined theoretical basis. Such a theory, once developed, would largely reside within Part 2 of the SEBoK. At present, Part 2 provides generalized foundations with pragmatic value to describe and improve current practice, and it will evolve to incorporate any emerging general theory of systems engineering as it becomes available.

The Systems Praxis Framework

The term systems praxis refers to the combined intellectual and practical effort to create holistic solutions to today’s complex challenges. Praxis means “translating an idea into action” (WordNet 2012), and in this context highlights the need to integrate appropriate theory with effective practice drawn from many different sources. Because complex challenges cut across disciplinary and organizational boundaries, systems praxis requires diverse communities to work together. To collaborate, they must first establish communication; and to communicate, they must first find shared points of connection.

To support this, members of the International Council on Systems Engineering (INCOSE) and the International Society for the Systems Sciences (ISSS), working through the International Federation for Systems Research (IFSR), developed the Systems Praxis Framework (IFSR 2012). This framework represents a first step toward a common language for systems praxis, and it has been adopted in the SEBoK as a way of organizing foundational knowledge. It helps make the concepts and principles of systems thinking and practice more accessible to anyone applying a systems approach to engineered system problems.

The Systems Praxis Framework highlights the flows and interconnections among elements of a broader knowledge ecosystem of systems theory and practice. This ecosystem situates systems engineering within an integrative context that links foundations, theories, representations, and approaches to practice.

Figure 2. The Systems Praxis Framework, Developed as a Joint Project of INCOSE and ISSS. (© 2012 International Federation for Systems Research) Released under Creative Commons Attribution 3.0 License. Source is available at http://systemspraxis.org/framework.pdf.

In this framework, the following elements are connected:

Systems Thinking is the core integrative element. It connects the foundations, theories, and representations of systems science with the hard, soft, and pragmatic approaches of systems practice. Like any discipline underpinned by science, systems praxis involves a continuous interplay between theory and practice: theory informs practice, and practice generates insights that refine theory. Systems thinking provides the ongoing capability to assess and appreciate the system context, and to guide appropriate adaptation throughout the praxis cycle.

Integrative Systems Science provides the conceptual base and is grouped into three broad areas:

• Foundations, organizing knowledge and supporting discovery (e.g., methodology, ontology, epistemology, axiology, praxiology, teleology, semiotics, category theory).
• Theories, abstracted from specific domains but universally applicable (e.g., general system theory, complexity, anticipatory systems, cybernetics, autopoiesis, living systems, design science, organization theory, systems pathology).
• Representations, models and formalisms for describing, analyzing, and predicting system behaviors and contexts (e.g., system dynamics, networks, cellular automata, life cycles, graphs, rich pictures, narratives, games, agent-based simulations).

Systems Approaches to Practice aim to act on real-world situations to produce desired outcomes while minimizing unintended consequences. No single branch of systems science or practice is sufficient for every problem; therefore, a pragmatic blend is often required:

• Hard approaches are suited to well-defined problems with clear goals and reliable data. They emphasize quantitative analysis, optimization, and technical systems, often grounded in “machine” metaphors.
• Soft approaches are suited to problems with incomplete data, ambiguous goals, and social complexity. They emphasize learning, communication, and multiple perspectives, drawing from “humanist” philosophies.
• Pragmatic approaches combine elements of both, selecting methods, tools, and heuristics as appropriate to the situation. This includes techniques such as boundary critique or model unfolding, enabling diverse stakeholders to make assumptions and constraints explicit.

The “clouds” that collectively represent systems praxis sit within a wider ecosystem of knowledge, learning, and action. Successful integration requires drawing on the sciences (e.g., physics, neuroscience), formal disciplines (e.g., mathematics, logic, computation), the humanities (e.g., psychology, culture, rhetoric), and pragmatic fields (e.g., accounting, design, law). Systems practice depends not only on theories and models, but also on data, metrics, local knowledge, and lived experience.

In summary, integrative systems science provides the concepts and patterns that allow us to understand complexity, while systems approaches to practice apply these insights to address real problems. Systems thinking binds them together, creating an adaptive cycle of theory and practice that underpins all systems engineering foundations.

Scope of Part 2

Part 2 of the SEBoK provides a guide to systems knowledge that is most relevant for understanding and practicing systems engineering. It does not attempt to capture the entirety of systems science or systems practice. Instead, it offers an overview of key aspects of systems theory and application that are especially important for systems engineers.

The organization of Part 2 is based on the Systems Praxis Framework (IFSR 2012), which emphasizes the need for a clear and shared foundation to support effective communication and collaboration across diverse domains. As the discipline evolves, it is expected that the coverage of systems knowledge in Part 2 will continue to expand.

The following diagram summarizes the way in which the knowledge in SEBoK Part 2 is organized..

Figure 3. The Relationships between Key Systems Ideas and SE. (SEBoK Original)

The six Knowledge Areas in Part 2 each highlight a different but complementary aspect of systems foundations:

1. Systems Fundamentals, introduces essential definitions, concepts, principles, and heuristics. These provide systems engineers with a baseline vocabulary and the means to distinguish different kinds of systems, including product, service, enterprise, and system-of-systems,
2. The Nature of Systems, surveys the diversity of natural, engineered, and socio-technical systems, drawing attention to universal patterns that underpin systems science and form the basis of systems thinking and systems engineering.
3. Systems Science, presents influential theories and movements in systems research, including the chronological development of systems knowledge and the foundations that inform systems approaches.
4. Systems Thinking, describes the perspectives, principles, and patterns that characterize a systemic worldview. It emphasizes the role of reflective practitioners who integrate research and practice in order to frame and address complex problems.
5. Representing Systems with Models, considers the central role of models in both advancing systems theory and supporting engineering practice, from conceptual understanding to design and analysis..
6. Systems Approach Applied to Engineered Systems, defines a structured approach for problem and opportunity discovery, solution synthesis, analysis, implementation, and use. This knowledge area provides the most direct link between systems foundations and practical SE application.

Taken together, these Knowledge Areas form a “system of ideas” that connects research, understanding, and practice. They provide a shared foundation of systems knowledge that underpins a wide range of scientific, management, and engineering disciplines, and that can be applied across all types of domains.

References

Works Cited

IFSR. 2012. The Systems Praxis Framework, Developed as a Joint Project of INCOSE and ISSS. Vienna, Austria: International Federation for Systems Research (IFSR). Available at: http://systemspraxis.org/framework.pdf.

Sillitto, H.G., 2012. "Integrating systems science, systems thinking, and systems engineering: Understanding the differences and exploiting the synergies", Proceedings of the 22nd INCOSE International Symposium, Rome, Italy, 9-12 July, 2012.

Primary References

Bertalanffy, L., von. 1968. General System Theory: Foundations, Development, Applications, rev. ed. New York, NY, USA: Braziller.

Checkland, P. B. 1999. Systems Thinking, Systems Practice. Chichester, UK: John Wiley & Sons.

INCOSE (2022). INCOSE Systems Engineering Vision 2025. San Diego, CA: International Council on Systems Engineering.

Additional References

Blanchard, B., & Fabrycky, W. (2010). Systems Engineering and Analysis (5th ed.). Saddle River, NJ: Prentice Hall.

Lawson, H. (2010). A Journey Through the Systems Landscape. London: College Publications.

Meadows, D. (2008). Thinking in Systems. White River Junction, VT: Chelsea Green.

Mobus, G. (2022). System Science: Theory, Analysis, Modeling and Design. Springer.

Ostrom, E. (2009). “A General Framework for Analyzing Sustainability of Social-Ecological Systems.” PNAS, 104(51): 15181–15187.

Senge, P.M. (1990). The Fifth Discipline: The Art & Practice of the Learning Organization. New York: Doubleday.

Troncale, L. (1985–2010). Selected works on Systems Isomorphies and Systems Processes.

Volk, T. (2017). Quarks to Culture: How We Came to Be. Columbia University Press.

Zwick, M. (2023). Elements and Relations: Aspects of a Scientific Metaphysics. Springer.

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SEBoK v. 2.13, released 17 November 2025