Introduction to Systems Engineering Fundamentals

This article forms part of the Systems Thinking Knowledge Area. It provides various perspectives on systems, including definitions, scope, and context. The basic definitions in this article are further expanded and discussed in Types of Systems and What is Systems Thinking?.

This article asks the following question: how can the many connotations of the word system in everyday use be turned into a theoretical framework capable of supporting the application of systems thinking in such a way that it can be usefully applied across all potential application domains and disciplines?

Systems Science View

The most basic ideas of a system whole can be traced back to the thinking of Aristotle and culminate in the works of the philosopher Hegel (M’Pherson 1974). Hegel’s view of holism states that an individual as part of an organic whole is fully realized only through his relationship to the whole. Humans have used this idea to help explain the relationships between abstract ideas by describing them as a system of related concepts, rules, or ideas. Some examples of such systems are the natural number system and political systems. The SEBoK uses the notion of a “system of ideas” to help present and explain system and systems engineering (SE) knowledge.

The generally agreed upon systems science definition of a system comes from General System Theory (GST) (Bertalanffy 1968) and considers a system as a set of related elements which form a coherent whole. The elements of a system may be not only conceptual organizations of ideals in symbolic form but also real objects; e.g., people, data, physical artifacts, etc. This definition includes the notion of a system of ideas, but also allows for the consideration of systems of things.

• Abstract systems contain only conceptual elements.
• Concrete systems contain at least two elements which are objects.

General System Theory considers the similarities between systems from different domains as a set of common system principles and concepts. A key notions of GST is that of those relationships which define membership of the system and thus define a system boundary For a closed systems all aspects of the system exist within this boundary. The boundary of an open systems defines those elements and relationships within a wider environment which can be considered part of the system and those which describe the interaction between system and environment. While systems thinking and the systems science and systems approaches arising from it, make extensive use of closed abstract systems of ideas they are focused on the understanding of open concrete systems within their environment.

The joining together of the various elements of a system can be related to either the structure of a system or to the behavior of a system. The structure of a system is its static existence, namely its elements and their relationships, whereas system behavior refers to the effect produced when an instance of the system is in operation. The actual behavior produced in operation leads to the fundamental property of emergence: “Whole entities exhibit properties which are meaningful only when attributed to the whole, not to its parts…” (Checkland 1999).

Laszlo summarizes the open system property of holism (or Systemic state) as a property of the system elements and how they are related in the system structure which leads them to create a cohesive whole (Laszlo 1972). Open Systems are formed when the relationships between the elements reach a balance or state in which elements form a boundary and structure which will remain stable within its environment. Laszlo describes three kinds of system response to change:

1. Adaptive self-regulation: All systems will tend to return to their previous state in response to external stimulus.
2. Adaptive self-organization: Some systems not only return to a previous state, but also reorganize to create new stable states which are more resistant to change.
3. Holon: Systems displaying characteristics one and two will tend to develop increasingly complex (hierarchical) structures.

Many of the original ideas upon which GST is based come from the study of systems in the biological and social sciences. Many natural systems and social systems are formed through the inherent cohesion between elements. Once formed, they will tend to stay in this structure, as well as combine and evolve further into more complex stable states to exploit this cohesion in order to sustain themselves in the face of threats or environmental pressures, as well as to produce other behaviors not possible from simpler combinations of elements. Natural and social systems can be understood through an understanding of this wholeness and cohesion. They can also be guided towards the development of behaviors which not only enhance their basic survival but also fulfil other goals or benefit to them or the systems around them. The Architecture of Complexity (Simon 1962) has shown that systems which evolve via a series of stable “hierarchical intermediate forms” will be more successful and adapt more quickly to environmental change.

At some point, the nature of the relationships between elements or of the behavior of the whole leads to complexity not associated with the elements themselves; this complexity can only be dealt with by considering the system as a whole.

Some systems are created by people for specific reasons and will need to not only exist and survive, but also achieve necessary outcomes.engineered systems can be deliberately created to take advantage of system properties such as holism and stability, but must also consider system challenges such as complexity and emergence.

Understanding these system concepts and associated principles forms the basis of systems thinking. An expanded discussion of these system concepts is given in Concepts of Systems Thinking.

System Definitions – a Discussion

How is a system defined in the SE literature? Systems engineers generally refer to their system of interest (soi) as “the system,” and their definitions of a “system” tend to characterize engineered systems . Two examples follow:

• “A system is an array of components designed to accomplish a particular objective according to plan” (Johnson, Kast, and Rosenzweig 1963).
• “A system is defined as a set of concepts and/or elements used to satisfy a need or requirement" (Miles 1973).

The INCOSE Handbook (2011) generalizes this idea of an engineered system as “an interacting combination of elements to accomplish a defined objective. These include hardware, software, firmware, people, information, techniques, facilities, services, and other support elements.”

However, engineered systems often find that their environment includes natural systems that don’t follow the definitions of a “system” above in that they have not been defined to satisfy a requirement or come into being to satisfy a defined objective. These include such systems as the solar system if one’s engineered system is an interplanetary spacecraft. This has led to more general definitions of a system following the systems science approach. For example, Aslaksen (2004) says a system consists of the following three related sets:

• a set of elements;
• a set of internal interactions between the elements; and
• a set of external interactions between one or more elements and the external world (i.e., interactions that can be observed from outside of the system).

This definition of a system enables people to reason about numerous classes of dynamic systems that involve engineered, social, and natural systems.

Fundamental properties of a system described in the SE literature include togetherness, structure, behavior, and emergence. These properties provide one perspective on what a system is. “We believe that the essence of a system is 'togetherness', the drawing together of various parts and the relationships they form in order to produce a new whole…” (Boardman and Sauser 2008). Hitchins (2009, 59-63) refers to this systems property as cohesion.

Natural systems and social systems often form part of the environment in which engineered systems need to exist. For a natural or social system, simply continuing to exist, and when appropriate, to adapt and grow, is sufficient. Man-made, engineered, and sociotechnical systems are created with a defined purpose (Hitchins 2009). Thus, these systems must not only be able to exist within their environment, but also do what is necessary to achieve their purpose.

System of Interest

As can be seen from the discussion above, most attempts to define the term “system” in SE either include assumptions about the system domain being considered, or are attempts to take a systems science view which risk becoming too abstract to be of practical use. A clear distinction is needed between defining "the system" to which a systems approach is applied and defining "systems" as an abstract idea which can be used to help understand complex situations.

The concept of a system helps make sense of the complexity of the real world. This is done either by creating an abstract system to help explain complex situations, such as the real number system, by creating a standardized approach to common problems, such as the Dewey Decimal System, or by agreeing on a model of a new situation to allow further exploration, such as a scientific theory or conceptual system design. People use systems to make sense of complexity in an individual way and when they work together to solve problems.

In the systems approach , a number of relevant systems may be considered to fully explore problems and solutions and a given element may be included in several system views. Thus, it is less important that “the system” can be defined than it is that combinations of systems can be used to help achieve engineering or management tasks.

The idea of a system context is used to define a system of interest (soi) , and to identify the important relationships between it, the systems it works directly with, and the systems which influence it in some way. This engineered system context relates to the systems science ideas of an open, concrete system, although such a system may include abstract system elements. There are a number of more detailed system concepts which the systems approach must also consider, such as static or dynamic, deterministic or non-deterministic, chaotic or homeostatic, complexity and adaptation, feedback and control, and more.

All applications of a systems approach (and hence of SE) are applied to an engineered systems context, and not to an individual system.

References

Works Cited

Alaksen, E. 2004. "A Critical Examination of the Foundations of Systems Engineering Tutorial". Paper presented at 14th Annual International Council on Systems Engineering (INCOSE) International Symposium, Toulouse, France, 20-24 June 2004.

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

Boardman, J. and B. Sauser. 2008. Systems Thinking: Coping with 21st Century Problems Boca Raton, FL, USA: Taylor & Francis.

Checkland, P. 1999. Systems Thinking, Systems Practice. New York, NY, USA: Wiley and Sons, Inc.

Hitchins, D. 2009. “What Are the General Principles Applicable to Systems?” INCOSE Insight, 12(4): 59-63.

INCOSE. 2011. INCOSE Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities, version 3.2.1. San Diego, CA, USA: International Council on Systems Engineering (INCOSE), INCOSE-TP-2003-002-03.2.1.

Johnson, R.A., F.W. Kast, and J.E. Rosenzweig. 1963. The Theory and Management of Systems. New York, NY, USA: McGraw-Hill Book Company.

Miles, R.F. (ed). 1973. System Concepts. New York, NY, USA: Wiley and Sons, Inc.

Laszlo, E., ed. 1972. The Relevance of General Systems Theory: Papers Presented to Ludwig von Bertalanffy on His Seventieth Birthday, New York, NY, USA: George Brazillier.

M’Pherson, P. K. 1974. "A perspective on systems science and systems philosophy". Futures. 6(3):219-39.

Simon, H. A. 1962. "The Architecture of Complexity." Proceedings of the American Philosophical Society, 106(6) (Dec. 12, 1962): 467-482.

Primary References

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

INCOSE. 2011. INCOSE Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities, version 3.2.1. San Diego, CA, USA: International Council on Systems Engineering (INCOSE), INCOSE-TP-2003-002-03.2.1.

Additional References

Hybertson, Duane. 2009. Model-oriented Systems Engineering Science: A Unifying Framework for Traditional and Complex Systems. Boca Raton, FL, USA: CRC Press.

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