1.1 WHAT IS SYSTEMS ENGINEERING?
There are many ways in which to define systems engineering. We will use the following definition:
To guide is defined as “to lead, manage, or direct, usually based on the superior experience in pursuing a given course” and “to show the way.” This characterization emphasizes the process of selecting the path for others to follow from among many possible courses – a primary function of systems engineering. A dictionary definition of engineering is “the application of scientific principles to practical ends; as the design, construction and operation of efficient and economical structures, equipment, and systems.” In this definition, the terms “efficient” and “economical” are particular contributions of good systems engineering. “Development” includes the identification, coordination, and management of diverse field of expertise in many domain applications.
The word “system,” as is the case with most common English words, has a very broad meaning. A frequently used definition of a system is “a set of interrelated components working together toward some common objective.” This definition implies a multiplicity of interacting parts that collectively perform a significant function. The term complex restricts this definition to systems in which the elements are diverse and have intricate relationships with one another. Thus, a home appliance such as a washing machine would not be considered sufficiently diverse and complex to require systems engineering, even though it may have some modern automated attachments. On the other hand, the context of an engineered system excludes such complex systems as living organisms and ecosystems. The restriction of the term “system” to one that is complex and engineered makes it more clearly applicable to the function of systems engineering as it is commonly understood.
The above definitions of “systems engineering” and “system” are not represented as being unique or superior to those used in other textbooks, each of which defines them somewhat differently. In order to avoid any potential misunderstanding, the meaning of these terms as used in this book is defined at the very outset, before going on to the more important subjects of the responsibilities, problems, activities, and tools of systems engineering.
Systems Engineering and Traditional Engineering Disciplines
From the above definition, it can be seen that systems engineering differs from mechanical, electrical, and other engineering disciplines in several important ways.
- Systems engineering is focused on the system as a whole; it emphasizes its total operation. It looks at the system from the outside, that is, at its interactions with other systems and the environment, as well as from the inside. It is concerned not only with the engineering design of the system but also with external factors, which can significantly constrain the design. These include the identification of customer needs, the system operational environment, interfacing systems, logistic support requirements, the capabilities of operating personnel, and such other factors as must be correctly reflected in system requirements documents and accommodated in the system design.
- While the primary purpose of systems engineering is to guide, this does not mean that systems engineers do not themselves play a key role in system design. On the contrary, they are responsible for leading the formative (Concept Development) stage of a new system development, which culminates in the functional design of the system reflecting the needs of the user. Important design decisions at this stage cannot be based entirely on quantitative knowledge, as they are for the traditional engineering disciplines, but rather must often rely on qualitative judgments balancing a variety of incommensurate quantities and utilizing experience in a variety of disciplines, especially when dealing with new technology.
- Systems engineering bridges the traditional engineering disciplines. The diversity of the elements in a complex system requires different engineering disciplines to be involved in their design and development. For the system to perform correctly, each system element must function properly in combination with one or more other system elements. Implementation of these interrelated functions is dependent on a complex set of physical and functional interactions between separately designed elements. Thus, the various elements cannot be engineered independently of one another and then simply assembled to produce a working system. Rather, systems engineers must guide and coordinate the design of each individual element as necessary to assure that the interactions and interfaces between system elements are compatible and mutually supporting. Such coordination is especially important when individual system elements are designed, tested, and supplied by different organizations.
Systems Engineering and Project Management
The engineering of a new complex system usually begins with an exploratory stage in which a new system concept is evolved to meet a recognized need or exploit a technological opportunity. When the decision is made to engineer the new concept into an operational system, the resulting effort is inherently a major enterprise, which typically requires many people, with diverse skills, to devote years of effort to bring the system from concept to operational use.
The magnitude and complexity of the effort to engineer a new system requires a dedicated team to lead and coordinate its execution. Such an enterprise is called a “project” and is directed by a project manager aided by a staff. Systems engineering is an inherent part of project management – the part that is concerned with guiding the engineering effort itself – setting its objectives, guiding its execution, evaluating its results, and prescribing necessary corrective actions to keep it on course. The management of the planning and control aspects of the project fiscal, contractual, and customer relations is supported by systems engineering, but is usually not considered to be part of the systems engineering function. This subject is described in more detail in Chapter 4
Recognition of the importance of systems engineering by every participant in a system development project is essential for its effective implementation. To accomplish this, it is often useful to formally assign the leader of the systems engineering team to a recognized position of technical responsibility and authority within the project.