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Introduction to Systems Engineering

This chapter focuses on the background of Systems Engineering, considering the history of the subject and why it is needed. This chapter will also provide an understanding of the main concepts associated with Systems Engineering and the terminology that will be adopted throughout this book, thus aiding our understanding of the topic as we progress. To do this, we will look at the following topics:

• A brief history of Systems Engineering
• Defining systems engineering
• The need for systems engineering

A brief history of Systems Engineering

It may be argued that Systems Engineering has been employed ever since mankind started building and developing complex systems. It could also be said that the pyramids in ancient Egypt are examples of complex systems, along with simple stone structures, such as henges, which may actually form part of a larger astrological system. Furthermore, mankind has observed complex systems such as the Solar System since the ancient Greeks first observed the motion of the planets and created the model of the geocentric universe.

In more recent times, the term Systems Engineering may be traced back to the early part of the 20th century in Bell Laboratories in the USA (Fagen, 1978). Examples of Systems Engineering may be observed in the Second World War, and the first attempt to teach Systems Engineering is claimed to have been in 1950 at MIT (Hall, 1962).

The 1960s saw the formulation of the field of study known as systems theory, which was first postulated by Ludwig von Bertalanffy (Bertalanffy, 1968) as "general systems theory."

The main tenet of systems theory is that it is a conceptual framework based on the principle that the component parts of a system can best be understood in the context of the relationships with each other and with other systems, rather than in isolation (Wilkinson, 2011). This is essential for all Systems Engineering as it means that elements in a System, or the systems themselves, are never considered by themselves but in relation to other elements or systems.

As systems became more complex, the need for a new approach to developing systems became more prevalent. Throughout the latter part of the 20th century, this need grew until it reached the point, in 1990, at which the National Council on Systems Engineering (NCOSE) was founded in the USA. Since then, this organization has evolved into the International Council on Systems Engineering (INCOSE), founded in 1995, which is the world's foremost authority on Systems Engineering and has over 70 chapters throughout the world.

Today, as the Complexity of the world that we live in and the systems that are being developed are increasing at an ever-expanding rate, there is an increased need for approaches that are rigorous and robust and can cope with these high levels of Complexity. Systems Engineering is such an approach.

Defining systems engineering

When considering Systems Engineering as a topic, it is important to understand exactly what is meant by the key terms that are being used. One aspect of all engineering (and all other professions, for that matter) that will emerge from this book very quickly is that there is seldom a single, definitive definition for any term. This creates a potential problem as communication, as will be discussed later in this chapter, is key to successful Systems Engineering.

In order to address this potential problem, this chapter will introduce, discuss, and define specific concepts and their associated terminology that will be used throughout the book. This will enable a Domain-Specific Language to be built up, which will then be used consistently throughout this book. Wherever possible and appropriate, the terminology adopted will be based on international best practices, including standards such as ISO 15288 (ISO, 2015), to ensure the provenance of the information presented here.

Defining a System

The first concept that will be discussed is that of a System. A System will be defined in different ways by different people, depending on the nature of the System. So, first of all, some types of Systems will be identified to illustrate some of the typical types of Systems that may be encountered in Systems Engineering.

There are many different classifications, or taxonomies, of Systems and one of the more widely accepted classifications is the one defined by Peter Checkland (Checkland, 1999), which is illustrated in the following diagram:

Figure 1.1: Checkland's five types of System

The diagram in Figure 1.1 shows Checkland's five types of generic Systems, which are as follows:

• Natural Systems, which represent open Systems whose characteristics are beyond the control of humans. Such Systems include weather systems, nature, the environment, time, and so on.
• Designed Physical Systems, which represent what most people would immediately think of when considering a System, such as smartphones, tablets, helicopters, cars, trains, planes, spaceships, boats, TVs, cameras, bridges, computer games, satellites, and even domestic appliances. The list is almost endless. The Systems will typically consist of physical artifacts that represent the real-world manifestation of the System.
• Designed Abstract Systems, which represent Systems that have no physical artifacts but that are used by people to understand or explain an idea or concept. Examples of such Systems include models, equations, thought experiments, and so on.
• Human Activity Systems, which are people-based Systems that can be seen or observed in the real world. These Systems will typically consist of different sets of people interacting to achieve a common goal or purpose. Examples of such Systems include a political system, social groups, people-based services, and so on.
• Transcendental Systems, which are Systems that go beyond our current understanding. Examples of such systems include deities, unknown problems, and Numberwang.

This is a good set of classifications, which we will use as a reference in this book. These classifications are a good way to think about different types of Systems, but the important point to understand here is that we can apply Systems Engineering to all five of these different categories of Systems.

Also, it should be kept in mind that it is possible to have systems that actually fit into more than one of these categories. Imagine, for example, a transport system that would have to take into account vehicles (Designed Physical Systems), operating models (Designed Abstract Systems), the environment (a Natural System), and a governing political system (a Human Activity System). In real life, the Complexity of Systems is such that it is typical, rather than unusual, to encounter examples of these Systems that can fit into multiple categories.

Characteristics of a System

The five different broad types of Systems have been introduced, but there is also a common set of characteristics that may be associated with all of these types of systems. These characteristics allow the Systems to be understood and developed. Let's explore these in the following sections.

System elements - characterizing System structure

Any system will have its own natural structure and may be thought of as a set of interacting System Elements, as shown in the following diagram:

Figure 1.2: Basic structure of a System - System Elements

The diagram in Figure 1.2 shows that a System is made up of a set of system elements and that there are two types of Systems: a System of Interest and an Enabling System. A System of Interest refers to a System that is under development, whereas an Enabling System refers to any System that has an interest in, or interacts with, a System of Interest.

One point to note here is that the structure of the System is actually more complex than this, as a System Element itself may be broken down into lower-level System Elements, which will lead to a System hierarchy of several levels being identified for a specific System. For the purposes of this initial discussion, the number of levels will be kept low in order to keep the explanations simple. Later in this book, when Systems are discussed in more detail, examples of hierarchies that span multiple levels will be considered.

The next key point for discussion here is that System Elements interact with other System Elements. This is a key concept in understanding true Systems and applying Systems Engineering. When considering any System, or System Element, it is important to understand that they will interact with other System Elements, rather than existing in isolation. In Systems Engineering, everything is connected to something else and so understanding the relationships between System Elements, which form the basis of the interactions between them, is just as important as understanding the System Elements themselves.

The interactions between System Elements also allow interfaces to be identified and defined between them. Understanding interfaces between System...