Systems Engineering Glossary

Here we have collected definitions of many of the terms and expressions used or referenced in the Systems Engineering Definitions


Transdisciplinarity is described in Wikipedia as an approach which “crosses many disciplinary boundaries to create a holistic approach.”  This emphasis on a holistic approach distinguishes it from cross-disciplinary, which focuses mainly on working across multiple disciplines while allowing each discipline to apply their own methods and approaches.  Systems engineering is simultaneously cross-disciplinary and transdisciplinary. (The cross-disciplinary aspect is discussed in the next section on the Integrative Approach.)

The transdisciplinary approach originated in the social sciences. It “transcends” all of the disciplines involved, and organizes the effort around common purpose, shared understanding and “learning together” in the context of real-world problems or themes. It is usable at any level, from complex to simple, from global to personal. A transdisciplinary approach is needed when the problem cannot readily be “solved” and the best that can likely be achieved is instead a “resolution.” The participants in the endeavour need to “transcend” their particular disciplinary approach to instead come to some overall useful compromise or synergistic understanding that their disciplines cannot come to on their own (even when working together in a normal integrative approach with other disciplines).

Madni A (2018)Transdisciplinary Systems Engineering: Exploiting Convergence in a Hyper-Connected World, Springer, 2018


The integrative approach has long been used in systems engineering and usually involves either interdisciplinary (e.g. integrated product teams) or multi-disciplinary (e.g. joint technical reviews) methods. The integrative approach by itself can be adequate where the situation is not overly complex and there are smaller numbers of stakeholders potentially impacted. The integrative approach can be used when dealing with a highly precedented situation that has been encountered before and a path to the solution can be readily identified and understood (albeit there will still be many challenges along the way, technical and otherwise). The integrative approach includes the traditional multi-disciplinary and inter-disciplinary approaches commonly used in systems engineering practice. The transdisciplinary approach may be needed in unprecedented situations or where there is a significant degree of complexity involved. See Madni (2018).

Successful realization

The successful realization of a system means that the system has been designed, implemented and put into use, satisfying the purposes for which it was intended.  Successful realization is often taken to mean that the cost and schedule of the development of the system were within acceptable limits, and the lifetime of the usefulness of the system is/will be long enough to meet customer and user expectations.


The retirement of a system happens when the system has reached the end of its useful life, or when it is deliberately taken out of use (perhaps because a different way has been developed to meet the needs the system was intended to satisfy, or because the resources needed to operate and support the system are no longer available).   Effective systems engineering provides ways to take the system out of use, and dispose appropriately of the elements of the system, so the system does not cause unintended problems after its useful life is finished.

Systems principles and concepts

Systems principles and concepts are the ways that systems thinking and the systems sciences infuse systems engineering.  Examples of some of the principles, concepts and supporting tools are: mental models, system archetypes, holistic thinking, separation of concerns, abstraction, modularity and encapsulation, causal loop diagrams, and systems mapping.  (The Systems Engineering Body of Knowledge describes many of these, and more, at and a paper presented at the 2019 INCOSE Symposium describes more: “Systems Engineering Principles: A Whitepaper” by the INCOSE Systems Engineering Principles Action Team led by Michael Watson).

Widest Sense

The widest sense of the use of the terms “engineering” and “engineered” means the terms are used to convey the meaning that encompasses the full array of activities the terms are used to refer to, across multiple disciplines and multiple applications areas.

Both ancient and modern definitions of Engineering allow for the wide interpretation intended here. For example, Google dictionary defines Engineering in two ways:

  1. the branch of science and technology concerned with the design, building, and use of engines, machines, and structures.
  2. the action of working artfully to bring something about.

And Wikipedia:

  • Engineering is the creative application of science, mathematical methods, and empirical evidence to the innovation, design, construction, operation and maintenance of structures, machines, materials, devices, systems, processes, and organizations.
  • The term engineering is derived from the Latin ingenium, meaning “cleverness” and ingeniare, meaning “to contrive, devise”.


An engineered system may be adapted when an existing system is being repurposed to meet needs different from those the system satisfied before it was adapted.  Natural systems which are modified to meet human aims are one kind of example of adapted systems (arguably a natural system has no purpose or goals, although it clearly has functionality).  For example, a river could be adapted to be part of a hydro-electric system.

Anticipated operational environment

The anticipated operational environment means the context or situation in which the system is planned to be used in practice (as contrasted with any situations used just for development or testing the system).

Intended purposes

The intended purposes of a physical system are the functions the system is planned by its procurers and designers to perform.  For a conceptual system, the intended purposes are the meanings the system is expected to convey.

Applicable constraints

The applicable constraints under which a system is expected to operate include all constraints imposed by the physical environment (such as the range of temperatures in which the system must operate), the constraints imposed by the user community (such as the skills levels of people who will operate the system), the constraints imposed by laws and regulations (such as the maximum permissible emissions of various toxic substances), and any constraints included by the customer as part of the requirements (such as the weight of the system, or the power consumed by the system).


The people component of an engineered system can be individuals, roles, organizations, organizational units, governance structures, or any other collection or organization of humans.


The products component of an engineered system can be hardware, software, firmware, data, facilities, etc.


The services component of an engineered system can be business services, information services, application services, infrastructure services, or any other service delivered by any combination of humans and technologies.

“Service” is intended to mean actions taken to satisfy needs of individuals or organizations.  The term service initially was used in the last century to describe actions which involved no tangible products at all. Early in this century (per Wikipedia at “managed services” emerged as a business model. The “service economy” (per Wikipedia at has resulted in an evolution in the meaning ascribed to “service”: “The old dichotomy between product and service has been replaced by a service-product continuum. Many products are being transformed into services. The Cambridge dictionary at says service is “work done or help provided, especially for the public or for a person or an organization.”


The information component of an engineered system can be individual information items, information categories, information structures, documentation, knowledge elements, ontologies, or any way data and meta-data is captured and stored.


The processes component of an engineered system can be procedures, methods, approaches, techniques, work instructions, policies, directives, or any other description of how people and/or systems can successfully accomplish activities.

Parts or elements

Parts or elements are used in this definition of system to mean the constituents of the system: the pieces, subsystems, models and/or other kinds of ingredients used to compose the system.

Natural elements

Natural elements of a system are those portions of the system which are being used or adapted from systems existing on the earth which were not originally developed by humans.  For example, in a hydro-electric system, a river used as a source of water and water pressure is a natural element.

Behavior or meaning

Behavior is intended to convey the functional activities of a system; that is, the actions the system takes which cause the results needed to satisfy the intended purposes of a physical system.

Meaning is intended to convey the communication of information needed to enable a conceptual system to satisfy its intended purposes.


Constituents of a system are the parts or elements of which the system is composed; the pieces, subsystems, models and/or other kinds of ingredients used to compose the system.

System’s properties

A system’s properties are the characteristics (including topology/interconnections of parts/elements, mass properties, organization/configuration, stability, controls, etc.) and behavior of the system.

Result or emerge

The behavior of a physical system and the “meaning” of a conceptual system result or emerge from the parts or elements composing the system and their individual properties and the relationships and interactions between and among the constituents (parts or elements), the system, and its environment.  The result is the outcome of the combination of the parts or elements and the interactions.  Unexpected behavior of the system may emerge from the parts, their interconnections, and the interactions when this behavior was not anticipated as the system was being designed.


Enterprise” is intended to mean a large undertaking, especially one of large scope, complication and risk – “a complex web of interactions distributed across geography and time” (Rebovitch & White, 2011). We do not just mean a large organization, since an enterprise often has multiple organizations that participate in the enterprise to the extent that each organization will derive some benefit from its participation. An enterprise is an endeavour usually requiring special initiative and boldness. Not all large activities are enterprises since their size does not necessarily entail taking large risk or dealing with a complicated situation.

Rebovitch & White (2010) Enterprise Systems Engineering – Advances in the Theory and Practice,p.4, CRC Press, Taylor & Francis, 2010

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