Types of Systems

This article forms part of the Systems Thinking Knowledge Area. It provides various perspectives on system classifications and types of system, expanded from the definitions in What is a System?.

The article defines the idea of an engineered system . Three specific types of engineered system context are generally recognized in systems engineering: product system , service system and enterprise system .

System Classification

A taxonomy is "a classification into ordered categories" (Dictionary.com 2011). Taxonomies are useful ways of organizing large numbers of individual items so their similarities and differences are apparent. Classification methods for systems have been proposed over the past forty years, yet no standard classification system exists.

The early developers of general system theory developed systems classification which has been the starting point for much of the subsequent work. Bertalanffy (Bertalanffy 1968) divided systems into 9 types, including control mechanisms, socio-cultural systems, open systems, and static structures. These classification approaches tend to focus on making sense of the natural and social world around us.

As system science moved away from the theory of systems and began to consider how this theory might be used to provide practical approaches and tools classification approaches began to separate human-designed from non-human-designed systems or natural from man-made systems (Magee and de Weck 2004). While they provide some methods for classifying natural systems, their primary emphasis and value to the practice of systems engineer is in their classification method for human-designed or man-made systems.

A discussion of and guide to the various classification methods proposed by systems scientists is included in History of Systems Science.

Types of Systems

The modern world has numerous kinds of systems that influence daily life. Some examples include transport systems, solar systems, telephone systems, the Dewey Decimal System, weapons systems, ecological systems, space systems, and so on; indeed it seems there is almost no end to the use of the word “system” in today’s society.

The classification methods above tend to classify systems either by the types of elements they contain or by their purpose.

A simple classification of system elements is:

• Natural Elements, objects or concepts which exist outside of any practical human control. Examples: the real number system, the solar system, planetary atmosphere circulation systems.
• Human Elements, either abstract human types or social constructs; or concrete individuals or social groups.
• Technological Elements, man made artifacts or constructs; including physical hardware, software and information.

Peter Checkland (Checkland 1999) proposed a classification of systems based on purpose into five classes: natural systems, designed physical systems, designed abstract systems, human activity systems and transcendental systems.

From this three related system domains are identified as follows and shown in Figure 1:

• A natural system is one whose elements are wholly natural.

• A social system includes only humans as elements.

• An engineered system is a man-made aggregation which may contain physical, informational, human, natural and social elements; normally created for the benefit of people.

These three types overlap to cover the full scope of real-world systems.

Figure 1.System Boundaries of Engineered Systems, Social Systems, and Natural Systems (Figure Developed for BKCASE)

natural systems are real world phenomena to which systems thinking is applied to help better understand what those systems do and how they do it. A truly natural system would be one that can be observed and reasoned about, but over which people cannot exercise control, such as the solar system.

social systems are purely human in nature, such as legislatures, conservation foundations, and the United Nations (UN) Security Council. These systems are human artifacts created to help people gain some kind of control over, or protection from, the natural world.

Note: from the definitions above Natural and Social Systems can contain only natural and human elements respectively. In reality, while it is possible to describe and reason about social systems, many of them rely on some interaction or relationship with engineered systems to fully realize their purpose and thus will form part of one or more engineered systems contexts.

engineered systems may be purely technical systems, such as bridges, electric autos, and power generation. Engineered systems which contain technical and either human or natural elements, such as water and power management, safety governance systems, dams and flood control systems, water and power safety assurance systems are often called sociotechnical systems . The behavior of such systems is determined both by the nature of the engineered elements, and by their ability to integrate with or deal with the variability of the natural and social systems around them. The ultimate success of any engineered system is thus measured by its ability to contribute to the success of relevant sociotechnical system contexts.

Wherever system elements are combined into an engineered system, the complexity of the resulting system will be increased. It is this increase in complexity that creates the need for a systems approach .

Groups of Systems

Systems can be grouped together to create more complex systems. In some cases it is sufficient to consider these systems as system elements in a higher level system, as part of a system hierarchy.

However, there are cases where the groupings of system produce an entity that must be treated differently from an integrated system. The most common groupings of systems that have characteristics beyond a single integrated system are systems of systems (sos) and federations of systems (fos) .

Maier examined the meaning of System of Systems in detail and used a characterization approach which emphasizes the independent nature of the system element, rather than “the commonly cited characteristics of systems-of-systems (complexity of the component systems and geographic distribution) which are not the appropriate taxonomic classifiers” (Maier 1998, 268).

A more detailed discussion of the different system grouping taxonomies developed by systems science can be found in Groupings of Systems.

Wherever independent systems are combined into groups the interaction between the systems adds a further complexity in particular by constraining how the resulting system can be changed or controlled. This dimension of complexity leads to the management and control aspects of the systems approach .

Engineered Systems Classifications

Engineered systems:

1. Are created, used and sustained to achieve a purpose, goal or mission that is of interest to an enterprise , team , or an individual.
2. Require a commitment of resources for development and support.
3. Are driven by stakeholders with multiple views on the use or creation of the system, or with some other stake in the system, its properties or existence.
4. Contain engineered hardware, software, people, services or a combination of these.
5. Exist within an environment that impacts the characteristics, use, sustainment and creation of the system.

Engineered systems typically:

1. Are defined by their purpose, goal or mission.
2. Have a life cycle and evolution dynamics.
3. May include human operators (interacting with the systems via processes) and other natural components that must be considered in the design and development of the system.
4. Are part of a system-of-interest hierarchy.

Historically, “Economists divide all economic activity into two broad categories, goods and services. Goods-producing industries are agriculture, mining, manufacturing, and construction; each of them creates some kind of tangible object. Service industries include everything else: banking, communications, wholesale and retail trade, all professional services such as engineering, computer software development, and medicine, nonprofit economic activity, all consumer services, and all government services, including defense and administration of justice....” (Encyclopedia Britannica 2011). A product or service is developed and supported by an individual, team, or enterprise. For example, express package delivery is a service offered worldwide by many enterprises, both public and private, both small and large; these services might use vehicle, communications or software products as needed.

The nature of engineered systems has changed dramatically over the past several decades from systems dominated by hardware (mechanical and electrical) to systems dominated by software. In addition systems that provide services, without delivering hardware or software, have become common as the need to obtain and use information has become greater. Recently organizations have become sufficiently complex that the techniques that were demonstrated to work on hardware and software have been applied to the engineering of enterprises.

Three specific types of engineered system context are generally recognized in systems engineering: product system , service system and enterprise system .

Products and Product Systems

The word product is define as "a thing produced by labour or effort; or anything produced" (Oxford English Dictionary). In a commercial sense a product is anything which is acquired, owned and used by an enterprise (hardware, software, information, personnel, an agreement or contract to provide something, etc.)

product systems are systems in which products are developed and delivered to the acquirer for the use of internal or external user. For product systems the ability to provide the necessary capability must be defined in the specifications for the hardware and software, or the integrated system that will be provided to the acquiring enterprise .

Services and Service Systems

A service can be simply defined as an act of help or assistance, or as any outcome required by one or more users which can be defined in terms of outcomes and quality of service without detail to how it is provided. e.g. transport, communications, protection, data processing, etc. Services are processes, performances, or experiences that one person or organization does for the benefit of another – such as custom tailoring a suit, cooking a dinner to order, driving a limousine, mounting a legal defense, setting a broken bone, teaching a class, or running a business’ information technology infrastructure and applications. In all cases, service involves deployment of knowledge and skills (competences) that one person or organization has for the benefit of another (Lusch and Vargo 2006), often done as a single, customized job. In all cases, service requires substantial input from the customer or client (Sampson 2001) – for example, how can a steak be customized unless the customer tells the waiter how the customer wants the steak prepared? (business/marketing science definition)

A service system is one that provides outcomes for a user without necessarily delivering hardware or software products to the service supplier. The hardware and software systems may be owned by a third party who is not responsible for the service. The use of service systems reduces or eliminates the need for acquirers to obtain capital equipment and software in order to obtain the capabilities needed to satisfy users.

Services have been part of the language of Systems Engineering for many years. The use of the term service system in more recent times is often associated with information system, i.e:

...unique features that characterize services – namely, services, especially emerging services, are information-driven, customer-centric, e-oriented, and productivity-focused. (Tien and Berg 2003, 13)

A more detailed discussion of the system theory associated with service systems can be found in History of Systems Science.

Enterprises and Enterprise Systems

An enterprise is one or more organizations or individuals sharing a definite mission, goals, and objectives to offer an output such as a product or service.

An enterprise system consists of a purposeful combination (e.g., network) of interdependent resources (e.g., people, processes, organizations, supporting technologies, and funding) that interact with 1) each other (e.g., to coordinate functions, share information, allocate funding, create workflows, and make decisions), and 2) their environment(s), to achieve (e.g., business and operational) goals through a complex web of interactions distributed across geography and time (Rebovich and White 2011, 4, 10, 34-35).

Both product and service systems require an enterprise system to create them and an enterprise to use the product system to deliver services either internally to the enterprise or externally to a broader community.

According to Maier’s definition, an enterprise would not necessarily be called a system of systems (sos) since the systems within the enterprise do not usually meet the criteria of operational and managerial independence. In fact, the whole purpose of an enterprise is to explicitly establish operational dependence between systems that the enterprise owns and/or operates in order to maximize the efficiency and effectiveness of the enterprise as a whole. Therefore, it is more proper to treat an enterprise system and an SoS as different types of things, with different properties and characteristics (DeRosa 2005).

Enterprise systems are unique, compared to product and service systems, in that they are constantly evolving, they rarely have detailed configuration controlled requirements, they typically have the goal of providing shareholder value and customer satisfaction, which are constantly changing and are difficult to verify, and they exist in a context (or environment) that is ill-defined and constantly changing.

Links to other areas of the SEBoK

SEBoK Part 4 Applications of Systems Engineering explores how systems engineering is applied differently in product, service, and enterprise systems. The notion of enterprises and enterprise systems permeates Part 5 Enabling Systems Engineering.

References

Works Cited

Bertalanffy, L. von. 1968. General System Theory. New York, NY, USA: Brazillier.

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

Dictionary.com, s.v. "Taxonomy," accessed September 7, 2011. Available at http://dictionary.reference.com/browse/taxonomy.

Encyclopedia Britannica, s.v. "Service Industry," accessed September 7, 2011. Available at http://www.britannica.com/EBchecked/topic/535980/service-industry.

DeRosa, J. K. 2005. “Enterprise Systems Engineering.” Air Force Association, Industry Day, Day 1, 4 August 2005, Danvers, MA. Available at: https://www.paulrevereafa.org/IndustryDay/05/presentations/index.asp.

Lusch, R.F. and S. L. Vargo (Eds). 2006. The service-dominant logic of marketing: Dialog, debate, and directions. Armonk, NY: ME Sharpe Inc.

Magee, C.L. and O.L. de Weck. 2004. "Complex System Classification". Proceedings of the Fourteenth Annual International Symposium of the International Council on Systems Engineering. June 20-24, 2004, Toulouse, France.

Maier, M., and E. Rechtin. 2009. The Art of Systems Architecting, 3rd Ed.. Boca Raton, FL, USA: CRC Press.

Rebovich, G., and B.E. White (eds.). 2011. Enterprise Systems Engineering: Advances in the Theory and Practice. Boca Raton, FL, USA: CRC Press.

Sampson, S.E. 2001. Understanding Service Businesses. New York, NY, USA: John Wiley.

Tien, J.M. and D. Berg. 2003. "A Case for Service Systems Engineering". Journal of Systems Science and Systems Engineering. 12(1): 13-38.

Primary References

Chang, C.M., 2010. Service Systems Management and Engineering: Creating Strategic Differentiation and Operational Excellence. Hoboken, NJ, USA: John Wiley and Sons.

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

Magee, C. L., O.L. de Weck. 2004. "Complex System Classification." Proceedings of the 14th Annual International Council on Systems Engineering International Symposium, 20-24 June 2004, Toulouse, France.

Rebovich, G., and B.E. White (eds.). 2011. Enterprise Systems Engineering: Advances in the Theory and Practice. Boca Raton, FL, USA: CRC Press.

Tien, J.M. and D. Berg. 2003. "A Case for Service Systems Engineering". Journal of Systems Science and Systems Engineering. 12(1): 13-38.

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This article was updated to include materials from 3 other 0.5 articles: The Product View of Engineered Systems, The Service View of Engineered Systems, and The Enterprise View of Engineered Systems. These articles have been folded into the current article and therefore are not included in 0.75. However, the review comments from 0.5 for the earlier articles can be seen below.

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