As a prelude, this first chapter will explicitly state the philosophical position followed in this book. The chapter starts by highlighting what is spontaneously thought under the term “CPS” to then argue the reasons why a general theory is necessary to build scientific knowledge about this object of inquiry and design. A brief historical perspective of closely related fields, namely control theory, information theory, and cybernetics, will also be given followed by a necessary digression of philosophical positions and possible misinterpretations of such broad theoretical constructions. In summary, the proposed demarcation can be seen as a risk management action to avoid mistakes arising from commonsense knowledge and other possible misconceptions in order to “clear the path” for the learning process to be carried out in the following hundreds of pages.
1.1 Cyber‐Physical Systems in 2020
Two thousand and twenty is a remarkable year, not for the high hopes the number 20‐20 brought, but for the series of critical events that have happened and affected everyone's life. The already fast‐pace trend of digitalization, which had started decades before, has boomed as a consequence of severe mobility restrictions imposed as a response to the COVID‐19 pandemics. The uses (and abuses) of information and communication technologies (ICTs) are firmly established and widespread in society. From dating to food delivery, from reading news to buying e‐books, from watching youtubers to arguing through tweets, the cyber world – before deemed in science fiction literature and movies as either utopian or apocalyptic – is now very concrete and pervasive. Is this concreteness of all those practices involving computers or computer networks (i.e. cyber‐practices) what defines CPSs? In some sense, yes; in many others, no; it all depends on how CPS is conceptualized! At all events, let us move step‐by‐step by looking at nonscientific definitions.
CPS is a term not broadly employed in everyday life. Its usage has a technical origin and is related to digitalization of processes across different sectors so that the term “CPS” has ended up being mostly used by academics in information technology, engineering, practitioners in industry, and managers. Such a broad concept usually leads to misunderstandings so much so that relevant standardization bodies have channeled efforts trying to establish a shared meaning. One remarkable example is the National Institute of Standards and Technology (NIST) located in the United States. NIST has several working groups related to CPS, whose outcomes are presented on a dedicated website [1]. In NIST's own words,
Cyber‐Physical Systems (CPS) comprise interacting digital, analog, physical, and human components engineered for function through integrated physics and logic. These systems will provide the foundation of our critical infrastructure, form the basis of emerging and future smart services, and improve our quality of life in many areas.
Cyber‐physical systems (CPS) will bring advances in personalized health care, emergency response, traffic flow management, and electric power generation and delivery, as well as in many other areas now just being envisioned. CPS comprise interacting digital, analog, physical, and human components engineered for function through integrated physics and logic. Other phrases that you might hear when discussing these and related CPS technologies include:
Internet of Things (IoT)
Industrial Internet
Smart Cities
Smart Grid
“Smart” Anything (e.g. Cars, Buildings, Homes, Manufacturing, Hospitals, Appliances)
As a commonplace when trying to determine the meaning of umbrella terms, the definition of CPS proposed by NIST is still too broad and vague (and excessively utopian) to become susceptible of scientific inquiry. On the other hand, such a definition offers us a starting point, which can be seen as the raw material of our theoretical investigation. A careful reading of the NIST text indicates the key common features of the diverse list of CPSs:
There are physical processes that can be digitalized with sensors or measuring devices;
These data can be processed and communicated to provide information of such processes;
These informative data are the basis for decisions (either by humans or by machines) of possible actions that are capable of creating “smartness” in the CPS;
CPSs are designed to intervene (improve) different concrete processes of our daily lives; therefore, they affect and are affected by different aspects of society.
Figure 1.1 Illustration of a CPS. Sensors measure physical processes, whose data are transmitted through a communication network. These data are then processed to support decisions related to the physical process by either a human operator or an expert system.
These points indicate generalities of CPSs, as illustrated in Figure 1.1. In most of the cases, though, they are only implicitly considered when particular solutions are analyzed and/or designed. As a matter of fact, specific CPSs do exist in the real world without the systematization to be proposed in this book. So, there is an apparent paradox here: on the one hand, we would like to build a scientific theory for CPSs in general; on the other hand, we see real deployments of particular CPSs that do not use such a theory. The next section will be devoted to resolve this contradiction by explaining the reasons why a general theory for CPS is necessary while practical solutions do indeed exist.
1.2 Need for a General Theory
The idea of having a general theory is, roughly speaking, to characterize in a nonsubjective manner a very well‐defined symbolic object that incorporates all the constitutive aspects of a class of real‐world objects and therefrom obtain new knowledge by both symbolic manipulation and experimental tests. This generalization opens the path for moving beyond know‐how‐style of knowledge toward abstract, scientific conceptualizations, which are essential to assess existing objects, design new ones, and define their fundamental limits.
Example 1.1 Chocolate cake. You would like to prepare the chocolate cake you ate in your childhood, whose recipe you found in the Internet. This instructs you how to make it. If you follow the instructions, you will have the cake you wish but without knowing why that specific combination of elements and the processes of mixing and cooking can produce such a cake. If you decide to investigate the recipe, you will find that different elements are compatible for chemical reasons, and, after processing then in a specific way, such a combination will have the desired flavor and structural characteristic. Based on this abstraction, you can now (i) understand the reasons why the recipe works, (ii) propose modifications to the recipe to make the cake fluffier or moister, and (iii) create a vegan version of the cake by finding replacement for milk, butter, and eggs.
This example serves as a very simplified illustration of the difference between technical knowledge (know‐how) and scientific knowledge. We are going to discuss sciences and scientific practice in more detail when pinpointing the philosophical position taken throughout this book. At this point, though, we should return to our main concern: the need for a general theory that conceptualizes CPSs. Like the particular chocolate cake, the existence of smart grids or cities, or even fully automated production lines neither precludes nor requires a general theory. Actually, their existence, the challenges in their particular deployments, and their specific operation can be seen as the necessary raw material for the scientific theory that would build
