Types of Systems

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. A brief discussion of classification approaches is given below.

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 manmade systems.

A discussion of and guide to the various classification methods proposed by systems scientists is included in History of System 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 into:

• Natural Elements, objects or concepts which exist outside of any 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 artefacts or constructs; including physical hardware, software and information.

Peter Checkland (Checkland 1999) proposed a classification of systems into five classes: natural systems, designed physical systems, designed abstract systems, human activity systems and transcendental systems. From this we can identify three related system domains 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 we apply systems thinking to help us better understand what they do and how they do it. A truly natural system would be a system we can observe and reason about, but over which we 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, are exclusively in the SS domain. These systems are human artifacts created to help us 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 System, many of them rely on some interaction or relationship with Engineered Systems to fully realise 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, and 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 in which they sit. The ultimate success of any engineered system is thus measured by its ability to contribute to the success of relevant sociotechnical system context.

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 systems become elements in a higher level system. However, there are cases where the groupings of system produce an entity that must be treated differently from a single 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 (glossary) in detail and used a characterization approach which emphasises 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) are not the appropriate taxonomic classifiers” (Maier 1998, 268).

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.

The systems approach includes models and activities useful in the understanding, creation, use and sustainment of Engineered Systems. Disciplines which use a systems approach (such as Systems Engineering) deal with the apparent System Context. This is done by creating a system context focused on a selected Engineered system of interest (soi) .

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.

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 systems is a system that provide 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.

Enterprises and Enterprise Systems

An enterprise system defines 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 (glossary) 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

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Primary References

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.

Paul, A. S. 1998. "Classifying Systems." Proceedings of the Eighth Annual International Council on Systems Engineering International Symposium, 26-30 July 1998, Vancouver, BC, Canada.

Gorod, A., B. Sauser, and J. Boardman. 2008. "System-of-Systems Engineering Management: A Review of Modern History and a Path Forward." IEEE Systems Journal. 2(4): 484-499.

Jamshidi, M. editor. 2009. Systems of Systems Engineering – Innovations for the 21st Century. Hoboken, NJ: Wiley and Sons.

Jamshidi, M. 2008. "System of Systems Engineering – New Challenges for the 21st Century". IEEE Aerospace and Electronic Systems Magazine. 23(5) (May 2008): 4-19.

Maier, M. W. 1998. "Architecting Principles for Systems-of-Systems". Systems Engineering. 1(4): 267-84.

Sage, A. and C. Cuppan. 2001. "On the Systems Engineering and Management of Systems of Systems and Federations of Systems". Information-Knowledge-Systems Management Journal. 2(4) (December 2001): 325-45.

Additional References

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