(Excerpt from, “What’s Size Got To Do With It,” IEEE-Wiley, by John Blyler)
The use of systems engineering to solve modern technical problems can be traced back to the early 1950s [10a], although its basic tenets rest on classical logic. Systems engineering is, basically, a rigorous method for focusing one’s attention
on the problem at hand. Its goal is to establish order out of seeming chaos by applying sound reasoning techniques. Systems engineering is a structured process used to transform operational needs into a documented system design. Its goal is to ensure that the end product of the engineered activity is something that meets the customer’s needs. That “something,” in this book, is
a rightsized computer system, and that “customer” is any user of the rightsized system.
What Is a System?
One definition of a system is “a collection of hardware, software, procedures, and people organized to accomplish some desired objectives.” In this viewpoint, a system is a goal-oriented collection of constituent parts known as subsystems. A subsystem, in turn, is made up of components, which can be divided into even smaller parts, known as elements (Fig. 2-1). It should be noted that the names given here for the hierarchy of entities that make up a system are not universal. Certain military standards , such as those dealing with systems of exceptionally large size, for example, an aircraft carrier, break a system down into a hierarchy of segments, groups, subsystems and, finally, components. Regardless of the terminology, systems are comprised of smaller constituent parts. The hierarchical approach will be used again and again in our discussion of systems engineering, not only to describe the structure of a system, but also to describe the discrete elements of such conceptual entities as functions, requirements, and solution architectures, which will be covered shortly. Such an approach involves the decomposition of the system
or conceptual entity.
Another, more robust way, to define a system emphasizes its functionality rather than its parts and components. This viewpoint is at the heart of the contemporary systems approach.
Systems Engineering Axiom 1: Parts are parts, but functions describe the whole.
The Systems Engineering Approach
Systems engineering provides a way to manage complexity by decomposing any system to a point at which the components can be easily understood and handled. Techniques are provided to ensure that necessary tasks are accomplished, at the right times, and for integrating the decomposed system back together to once again form a whole.
The key elements of systems engineering are integration, life cycle, teamwork, and tailoring:
- Systems engineering is “good” engineering practices integrated across all disciplines, at every level of system detail, and throughout the life cycle of the system. The key word is integrated. Many organizations have good engineering practices in specific areas, but not as an integrated whole. Fully integrated systems reduce duplication and rework, and ensure that the effects of change can be traced throughout a system.
- Systems engineering is a process that takes places throughout the life cycle of the system, from womb to tomb, from cradle to grave. It begins with the first inkling of a problem and does not end until the solution is implemented and operated throughout a useful life span.
- Systems engineering is a team effort. It is not the sole responsibility of a single person, group, or department, but must permeate an organization. Systems engineering relies on an interdisciplinary team whose efforts are orchestrated by a cognizant systems engineer.
- Finally, systems engineering activities must be tailored to every organization, to every task, and to every phase of the life cycle. Each rightsizing project has special aspects that require adaptations of the general approach.
The Systems Approach
Systems engineering distinguishes itself from the traditional engineering disciplines by the application of systems theory. In the systems approach, a system is viewed in terms of the functions that it must perform, instead of in terms of the parts of which it is comprised (see , ). This emphasis on functionality represents a significant change from the traditional design engineering viewpoint, where a system is described in terms of its constituent parts. The systems approach is based, in part, on the observation that even when the parts of a system are performing well individually, the system, as a whole, may be performing poorly.
Thus, the systems approach emphasizes the functioning of the entire system. Systems engineering uses the systems approach to analyze and develop the functions that a desired system must perform in order to meet a customer’s needs. But systems engineering encompasses many other activities as well, including risk management, decision analysis, and configuration control.
The traditional engineering disciplines consist of electrical, mechanical, chemical, civil, agricultural, and industrial engineering . Systems engineering, when applied properly, incorporates the best practices of all these disciplines, including a structured approach to problem solving. But unlike the other engineering fields, systems engineering is not based on natural laws, such as those in physics or chemistry. Instead, systems engineering evolved from studies of the interactions of various scientific and sociological systems.
Systems engineering is also different from the traditional engineering in its emphasis on functionality at every level of system detail and throughout the life cycle. Also systems engineers conceptualize a system in terms of inputs and outputs,
where a function transforms a given input to a given output.
Six Basic Steps of the Systems Engineering Approach
There are six basic steps to follow in using a systems engineering approach: (See Part II) …