Systems engineering

Systems engineering (or systems design engineering) as a field originated around the time of World War II. Large or highly complex engineering projects, such as the development of a new airliner or warship, are often decomposed into stages and managed throughout the entire life of the product or system. This process of managing the system's life cycle (through concept, design, production, operation and disposal) is a bit like executing a series of interconnected engineering projects in a sequence, each project drawing on the results of the last until the end result is achieved.

This approach to engineering systems is inherently complex, since the behavior of and interaction between system components is not always clearly defined. Defining and characterizing such complex systems is the primary aim of systems engineering.

Admiral Grace Hopper has been quoted as saying "Life was simple before World War II. After that, we had systems."



There are several methods and tools that are frequently used by systems engineers:

  • requirements capture
  • systems architecture and design
  • interface design and specification
  • communications protocol design and specification
  • simulation and modeling
  • acceptance testing
  • verification, validation and fault modeling


The first significant systems engineering was performed for telephone systems. All the different parts of the phone system have to interoperate reliably. An excellent overview of the interfaces and logic, with some history, is "Digital Telephony" by John C. Bellamy. For operational telephony terms, see Newton's Telecom Dictionary, for example.


In recent times, industry in general has begun to accept that the engineering of systems, both large and small, can lead to unpredictable behavior and the emergence of unforeseen system characteristics. Decisions made at the beginning of a project whose consequences are not clearly understood can have enormous implications later in the life of a system, and it is the task of the modern systems engineer to explore these issues and make critical decisions. There is no method which guarantees that decisions made today will still be valid when a system goes into service years or decades after it is first conceived but there are techniques to support the process of systems engineering. Examples include the use of soft systems methodology, Jay Wright Forrester's System dynamics method and the Unified Modeling Language (UML), each of which are currently being explored, evaluated and developed to support the engineering decision making process.

Systems engineering often involves the modelling or simulation of some aspects of the proposed system in order to validate assumptions or explore theories. For example, highly complex systems such as aircraft are usually modeled and simulated before flight. In this way the initial aeroelastic engineering and control equations can be drafted initially and improved before the physical system is constructed. Since aircraft are often very expensive, this reduces the expense and difficulty of debugging the controls and reduces the risk of crashing real aircraft. Careful initial testing and flight envelope expansion are typically still required to reach acceptable levels of safety and performance in advanced aircraft.

System engineers perform testing and validation when a system has to have predictable behavior. For example medical machinery such as heart and lung machines usually consist of several parts, engineered by different companies. Testing and validation assures that normal operation and possible failures of each part will not harm the patient. Other applications are communications systems, or banking software, where failures can cause loss of property or liability. Test plans can often be adjusted to save significant amounts of money, by testing partial systems, or including special features in a system to aid testing.

Subfields of systems engineering

While it is obvious that a great many specialist or "niche" areas within the discipline of Engineering may be considered to be subfields of Systems Engineering, the increasing diversity and complexity inherent in today's systems has established a greater degree of distinction between these areas. Many subfields may be considered on their own merits as opposed to existing only as a subset of a more general subject. Indeed, many of these specialisms have contributed to the development of Systems Engineering as a distinct entity, researched and refined separately from those described here. Software engineering, for example, has helped to shape the modern perception of Systems Engineering.

Safety engineering

The techniques of safety engineering can be applied by everyday people to planning complex events to assure that the systems cannot cause harm. Most of safety engineering is just a way of making plans that cope with failures.

Usually a failure in safety-certified systems is acceptable if less than one life per 30 years of operation (10^9 hours) is lost to mechanical failure. Most Western nuclear reactors, medical equipment and commercial aircraft are certified to this level. This level is accepted not because loss of life is acceptable, but rather because a design near this level usually has significant mechanical redundancy, and the failures will be gradual enough that repairs can be scheduled before significant loss of life can occur.

Reliability engineering

Reliability engineering is the discipline of ensuring a system will be reliable, i.e., failure-free, when operated in a specified manner. Reliability engineering is performed throughout the entire life cycle and relies heavily on statistics, probability theory and reliability theory. Reliability engineering applies to the entire system, including hardware and software. It is closely associated with maintainability engineering and logistics engineering. Some reliability engineering techniques overlap safety engineering techniques, such as the failure modes and effects analysis.

Interface design

Interface design and specification are concerned with making the pieces of a system interoperate. For example, the plugs between two computer systems can be a fertile source of failures. Sometimes something as simple as gold-plating the plugs can lower the probability of a failure enough to save millions of dollars.

Another issue is assuring that the signals that pass from system to the next are in tolerance, and that the receivers have a wider tolerance than transmitters. Another issue is that the interface should be able to accept new features. Most often this is a problem in a plug and jack, of the transmission speed, although it sometimes affects computer data formats. The rule of thumb is that roughly 20% of the space in an interface should be reserved for future additions.

Human-Computer Interaction (HCI) is another aspect of interface design and is a vital part of modern Systems Engineering when considering the user of a system.

Cognitive Systems Engineering

Cognitive Systems Engineering is Systems Engineering with the human integrated as an explicit part of the system. It depends on the direct application of centuries of experience and research in both Cognitive Psychology and Systems Engineering. Cognitive Systems Engineering focuses on how man interacts with the environment and attempts to design systems that explicitly respect how humans think. Cognitive Systems Engineering works at the intersection of: (1) the problems imposed by the world, (2) the needs of agents (both human and software), and (3) the interaction with the various systems and technologies to affect the situation.

Sometimes referred to as Human Engineering, this subject also deals with ergonomics in system design.

Communication protocols

Interface design principles also have been used to place reserved wires, plug-space, command codes and bits in communication protocols. Systems engineering principles are applied in the design of network protocols.

Security engineering

Security engineering can be viewed as a field of systems engineering.

Educational institutions

There are many universities that now offer industrial or systems engineering programs, and most engineering programs are changing towards an overall "systems" approach to analysis and design.

One university program, the systems design engineering program at the University of Waterloo in Ontario, Canada is notable for being one of the few that has been teaching students how to solve problems with large scale systems. Due to the challenge of teaching engineering at this scale, and also requiring students to have all the other skills necessary for effectively applying this (for example a very broad technical skill-set and strong leadership skills), the program recruits some of the best high school gradutes every year.

Another institution, Cranfield University in the UK, offers an MSc in Systems Engineering for Defence. This course explores the many facets of large scale systems procurement.

Southern Methodist University in Dallas, Texas offers MS and PhD degrees in Systems Engineering, with concentrations in Logistics, Reliability, Systems Analysis, Management and Leadership. These programs are particularly tailored to suit the needs of the large aerospace defense companies in the North Texas area, such as Lockheed Martin, Raytheon and Bell Helicopter.

External links

Universities that offer Systems Engineering Degrees

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