Ian Faulconbridge - Introduction to Systems Engineering

Before we begin to address thediscipline associated with engineering a system, we need to consider what ismeant by a system. There are physical systems such a solar systems, riversystems, railway systems, satellite systems, communication systems, informationsystems, pulley systems, nervous systems, just to name a few. There arephilosophical systems, social systems, religious systems, gambling systems,banking systems, systems of government, and many more. Before we continue,therefore, we should briefly consider what we mean by a system in thecontext of systems engineering.

ISO/IEC 15288 defines a system asa combination of interacting elements organized to achieve one or morestated purposes .As illustrated in Figure 1-1, the very act of identifying the system thatwe are interested in, implies an external system boundary and a systemof interest (SOI).

Figure 1-1. An SOI: its elements, interconnections, and boundary.

The purpose of the system is called its missioninthe broadest sense, the mission of the system is to provide a solution to a businessproblem. When we refer to a system as comprising system elements thatare interconnected in order to achieve the systems mission, weimply that all three of those principal aspects result from conscious choice.That is, we are referring to systems that have been deliberately designed,or engineeredhence our interest in systems engineering. Further,a system that has been engineered to perform a specified mission must be ableto perform that mission with relative autonomythat is, it must be manageriallyand operationally independent (and may well have been procured independently).

There are numerous ways to classifysystemshere we identify the four main types in order to be clear as to whichtype of system we refer to in this book:

Closed/open systems. An open system interacts with itsoperating environmentit accepts inputs from that environment across itsboundary and returns outputs across the same boundary to the externalenvironment. A closed system is isolated from its external environment. We areonly interested in useful systems, which are therefore open.

Natural/human-made/human-modified systems. Natural systemscontain natural elements that result from natural processes; human-made systemscome into existence through the efforts of humans and may contain human-madeelements or natural elements adapted to human-designed purposes. Naturalsystems that have been modified for human purposes are called human-modifiedsystems. The systems engineering for natural systems is certainly not conductedby humans, so we are only interested in human-made/modified systems.

Physical/conceptual systems. Physical systems exist in aphysical form; conceptual systems do not have a physical form. We focus here onphysical systems.

Precedented/unprecedented systems. In a precedented system,similar such systems (or, at least, the majority of system elements) have beenproduced before. An unprecedented system is one that has not been previouslyproduced. Systems that comprise mostly unprecedented elements are the result ofresearch and development effort. Here we focus on systems that comprise largelyprecedented elementsthat is, those to which engineering is appropriate.

A wide variety of combinations ofthe above (and other) characteristics can lead to a large number of types ofsystems, each of which has markedly difficult properties. In systemsengineering we are interested in open, physical systems that are human-made/modifiedfrom largely precedented elements.

Now, since we are interested in engineeringphysical systems that are open, our SOI must accommodate externalinterfaces(inputs/outputs) across the system boundary to external elements thatexist in an external operating environment (or perhaps in a relatedsystem)see Figure 1-2.

Figure 1-2. An SOI: its elements, interconnections, boundary, and interfaces to externalelements in the operating environment.

In a physical sense, the term systemis sometimes considered to be synonymous with productthat is, we saythat the project is delivering a system, or is delivering a product. A systemis normally, however, considered to comprise a number of products such asoperational products (end products) and enabling products (such as test,training, and disposal products).

Before we go any further, however, wemust acknowledge that the systems we are interested in are much more than anaggregation of hardware or software products and must also be described interms of all of its constituent elements, including: the major hardware andsoftware products, the organisation within which it will be fielded, thepersonnel who will interact with it in many ways, the collective trainingsystems required, as well as the facilities, data, and support (includingsupplies) required to keep the system in service, and the operating proceduresand organisational policies. The system is fully defined by the combination ofthese resources operating in its operational environment in order to achievesome purpose. In that sense then, we could define a system as delivering an