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Analysis and Design
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
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
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
- 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
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
- 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.
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
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.
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