Types of Systems

The word “system” is so commonly and widely used that it provides little information. Systems engineers typically need to consider the type of system before starting work. Classification methods have been proposed over the past forty years, yet no standard classification system has been defined or accepted. The various methods that have been proposed are summarized in this article. However, systems engineers must define an appropriate classification system that fits their current situation.

Classification Methods

A search of systems engineering textbooks and technical papers yields a limited amount of information on classification methods applied to systems and systems engineering. Less than ten experts have addresses this subject. No consensus has emerged on classification methods. This article provides a high level overview of the approaches proposed, some of their significant features and references to the more detailed information that is currently available. Peter Checkland (1971, 671) proposed one of the earliest classification systems. It provides a basic and useful classification of systems. Arthur Paul (1998) surveyed the work to date and proposed methods for classifying systems. The most recent work was performed by Magee and de Weck (2004) who developed a classification approach for complex systems and focused on engineered systems.

All of these classification approaches separate human-designed from non-human-designed systems or natural from manmade systems. While they provide some methods for classifying natural systems their primary emphasis, and value to the practicing systems engineer, is in their classification for human-designed or manmade systems. Peter Checkland proposed five classifications: natural systems, designed physical systems, designed abstract systems, human activity systems and transcendental systems. The first two classifications are self explanatory.

Designed abstract systems – These systems do not contain any physical artifacts but are designed by humans to serve some explanatory purpose.

Human activity systems – These systems are observable in the world of innumerable sets of human activities that are more or less consciously ordered in wholes as a result of some underlying purpose or mission. At one extreme is a system consisting of a human wielding a hammer. At the other lie international political systems.

Transcendental systems – These are systems that go beyond the aforementioned four systems classes, systems beyond knowledge.

Checkland refers to these five systems as comprising a “systems map of the universe”. (1999, p.111)

Peter Checkland, starting himself from a systems engineering perspective, successively observed the problems in applying a systems engineering approach to the more fuzzy, ill-defined problems found in the social and political arenas. (1999, p. A9) Thus he introduced a distinction between hard systems and soft systems:

Hard systems of the world are characterized by the ability to define purpose, goals, and missions that can be addressed via engineering methodologies in attempting to, in some sense, “optimize” a solution.

Soft systems of the world are characterized by extremely complex, problematical, and often mysterious phenomena for which concrete goals cannot be established and which require learning in order to make improvement. Such systems are not limited to the social and political arenas and also exist within and amongst enterprises where complex, often ill-defined patterns of behavior are observed that are limiting the enterprise's ability to improve.

The systems engineering discipline is primarily aimed at developing, modifying or supporting hard systems.

Magee and de Weck examine many possible methods that include: degree of complexity, branch of the economy that produced the system, realm of existence (physical or in thought), boundary, origin, time dependence, system states, human involvement / system control, human wants, ownership and functional type. They conclude by proposing a functional classification method that sorts systems by their process: transform, transport, store, exchange, or control and by the entity that they operate on: matter, energy, information and value.

Other categorizations of system types can be found throughout the literature. The varieties of suggested types that relate to specific presentations of various authors include:

Aslaksen (1996) describes three main classes of systems, according to the actions they perform: transport systems (translations in space), storage systems (translations in time), and production systems (time and space independent transformations). Blanchard (2005) describes several types including human-made systems, physical systems, conceptual systems, static systems, closed systems and open systems. Giachetti (2009) describes enterprise systems. Jackson (2010) describes technological (or product) systems, product-centered infrastructure systems, technological system with human interface, human-intensive systems, process systems, socio-ecological systems, complex adaptive systems and infrastructure systems. Maier (2009) describes builder-architected systems, form-first systems, politico-technical systems and socio-technical systems. Wasson (2006) describes cultural systems, business systems, educational systems, financial systems, government systems, medical systems and transportation systems.

The reader is encouraged to follow up on these sources in order to provide a deeper perspective of the various categorizations of system types.

System Classifications

The generally accepted, although there is no consensus, and useful classifications that should be considered are:

Natural or Manmade
Physical or Abstract / Conceptual
Classification by complexity – simple, complicated and complex
Hard or Soft
Static or Dynamic
Classification by function or domain

The systems engineering profession is usually involved with manmade, physical, complicated to complex, hard, dynamic systems with wide range of functions useful to mankind in many domains. As the profession evolves the range of system types has increased with many recent developments aimed at complex systems and systems with more natural components. Some aspects of systems engineering have been applied to observing natural systems, such as weather modeling and prediction. In these cases the model is typically viewed as the system being developed with the goal of making the model match the natural system. In these cases classifications of natural systems may be necessary and additional work may be needed.

References

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Citations

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Primary References

Aslaksen, E.W. 1996. The Changing Nature of Engineering. New York, NY: McGraw-Hill.]]

Blanchard, B. S., and W. J. Fabrycky. 2005. Systems engineering and analysis. Prentice-hall international series in industrial and systems engineering. 4th ed. Englewood Cliffs, NJ, USA: Prentice-Hall.

Checkland, P. B. 1999. Systems thinking, systems practice. Chichester, UK: John Wiley & Sons Ltd.

Giachetti, R. E. 2009. Design of enterprise systems: Theory, architectures, and methods. Boca Raton, FL, USA: CRC Press.

Magee, C. L., de Weck, O. L., 2004. Complex System Classification, Fourteenth Annual International Symposium of the International Council on Systems Engineering (INCOSE), 20 June – 24 June 2004

Maier, M., and E. Rechtin. 2009. The art of systems architecting. 3rd ed. Boca Raton, FL, USA: CRC Press.

Paul, A. S. 1998. Classifying Systems, Proceedings of the eighth annual International Symposium of the International Council on Systems Engineering (INCOSE).

Wasson, C. S. 2006. System analysis, design and development. Hoboken, NJ: John Wiley and Sons Ltd.