What is a System?

The term “system” originates from the Greek term syst¯ema, which means to “place together.” Multiple business and engineering domains have definitions of a system. This text defines a system as:

System An integrated set of interoperable elements, each with explicitly specified and bounded capabilities, working synergistically to perform value-added processing to enable a User to satisfy mission-oriented operational needs in a prescribed operating environment with a specified outcome and probability of success.

To help you understand the rationale for this definition, let’s examine each part in detail.

System Definition Rationale

The definition above captures a number of key discussion points about systems. Let’s examine the basis for each phrase in the definition.

By “an integrated set,” we mean that a system, by definition, is composed of hierarchical levels of physical elements, entities, or components.
By “interoperable elements,” we mean that elements within the system’s structure must be compatible with each other in form, fit, and function, for example. System elements include equipment (e.g., hardware and system, system, facilities, operating constraints, support), maintenance, supplies, spares, training, resources, procedural data, external systems, and anything else that supports mission accomplishment.

One is tempted to expand this phrase to state “interoperable and complementary.” In general, system elements should have complementary missions and objectives with nonoverlapping capabilities. However, redundant systems may require duplication of capabilities across several system elements. Additionally, some systems, such as networks, have multiple instances of the same components.

By each element having “explicitly specified and bounded capabilities,” we mean that every element should work to accomplish some higher level goal or purposeful mission. System element contributions to the overall system performance must be explicitly specified. This requires that operational and functional performance capabilities for each system element be identified and explicitly bounded to a level of specificity that allows the element to be analyzed, designed, developed, tested, verified, and validated—either on a stand-alone basis or as part of the integrated system.
By “working in synergistically,” we mean that the purpose of integrating the set of elements is to leverage the capabilities of individual element capabilities to accomplish a higher level capability that cannot be achieved as stand-alone elements.
By “value-added processing,” we mean that factors such operational cost, utility, suitability, availability, and efficiency demand that each system operation and task add value to its inputs availability, and produce outputs that contribute to achievement of the overall system mission outcome and performance objectives.
By “enable a user to predictably satisfy mission-oriented operational needs,” we mean that every system has a purpose (i.e., a reason for existence) and a value to the user(s). Its value may be a return on investment (ROI) relative to satisfying operational needs or to satisfy system missions and objectives.
By “in a prescribed operating environment,” we mean that for economic, outcome, and survival reasons, every system must have a prescribed—that is, bounded—operating environment.
By “with a specified outcome,” we mean that system stakeholders (Users, shareholders, owners, etc.) expect systems to produce results. The observed behavior, products, byproducts, or services, for example, must be outcome-oriented, quantifiable, measurable, and verifiable.
By “and probability of success,” we mean that accomplishment of a specific outcome involves a degree of uncertainty or risk. Thus, the degree of success is determined by various performance factors such as reliability, dependability, availability, maintainability, sustainability, lethality, and survivability.

You need at least four types of agreement on working level definitions of a system:

a personal understanding
a program team consensus
an organizational (e.g., System Developer) consensus, and
most important, a contractual consensus with your customer.

Why? Of particular importance is that you, your program team, and your customer (i.e., a User or an Acquirer as the User’s technical representative) have a mutually clear and concise understanding of the term. Organizationally you need a consensus of agreement among the System Developer team members. The intent is to establish continuity across contract and organizations as personnel transition between programs.

Other Definitions of a System

National and international standards organizations as well as different authors have their own definitions of a system. If you analyze these, you will find a diversity of viewpoints, all tempered by their personal knowledge and experiences. Moreover, achievement of a “one size fits all” convergence and consensus by standards organizations often results in wording that is so diluted that many believe it to be insufficient and inadequate. Examples of organizations having standard definitions include:

International Council on Systems Engineering (INCOSE)
Institute of Electrical and Electronic Engineers (IEEE)
American National Standards Institute (ANSI)/Electronic Industries Alliance (EIA)
International Standards Organization (ISO)
US Department of Defense (DoD)
US National Aeronautics and Space Administration (NASA)
US Federal Aviation Administration (FAA)

You are encouraged to broaden your knowledge and explore definitions by these organizations. You should then select one that best fits your business application. Depending on your personal viewpoints and needs, the definition stated in this text should prove to be the most descriptive characterization.

Closing Point

When people develop definitions, they attempt to create content and grammar simultaneously. People typically spend a disproportionate amount of time on grammar and spend very little time on substantive content. We see this in specifications and plans, for example. Grammar is important, since it is the root of our language and communications. However, wordsmithed grammar has no value if it lacks substantive content.

You will be surprised how animated and energized people become over wording exercises. Subsequently, they throw up their hands and walk away. For highly diverse terms such as a system, a good definition may sometimes be simply a bulleted list of descriptors concerning what a term is or, perhaps, is not. So, if you or your team attempts to create your own definition, perform one step at a time. Obtain consensus on the key elements of substantive content. Then, structure the statement in a logical sequence and translate the structure into grammar.