Читать книгу Cyber-physical Systems - Pedro H. J. Nardelli - Страница 24

The definition of a particular system is usually arbitrary or assumed as given. When someone talks about a car, anyone listening should have a very clear idea about that system. But, this might be a trick: is a car without an engine, or wheels, still a car? Similar kinds of discussions are very common in other domains as well. For example: should an oat‐based drink be called oat milk?

In the legal domain, this definition is normative, usually as result of a deliberative process so that a definition can be imposed to indicate which is the correct word to name a given thing. The same happens with the word “car.” Each country has its own legal definition of what is considered a “car” indicating who is eligible to drive, or what taxes are to be paid. However, as we have discussed in the previous chapter, scientific concepts are different from words used in other practices: the former exist in a specific theoretical discourse whose meaning is completely defined by the formal structure of the theory they are part of. The scientific meaning of the word “car” then needs to be very well‐defined if it is to be considered a scientific concept. The question remains: how could such a theoretical concept be defined? The answer, once again, might be elusive: it depends on the scientific theory you are dealing with.

Since this chapter is about systems and how to scientifically define particular systems, our answer to that question will follow the solution we offer to the demarcation problem, where the system boundaries need to be defined with respect to everything else, which is referred to as environment. In other words, the problem is how to draw a line of demarcation between the system and the environment. This demarcation should not only indicate a functional relation but also a structural one. In this sense, the demarcation problem concerns both (i) how the system functions and (ii) how it is articulated with the environment so that its functioning can endure.

Definition 2.3 Demarcation problem The demarcation problem refers to the determination of the boundaries that constitute a particular system as such in relation to everything else, i.e. the environment, as well as the specific articulations between the system and the environment.

This definition indicates the theoretical challenges ahead of us. Two remarks are important: (i) the solution of the demarcation problem determines at the same time what is internal to a particular system, and what is not, and (ii) from the proposed demarcation, the articulations and interactions between that particular system and everything else need to the determined, which also determines its level of autonomy. Clearly, other systems are also part of the environment, as well as other instances of reality that affect and are affected by such a particular system under investigation. Looking at the broader picture without specifying any particular system, we see a whole that is constituted by several systems that are related to each other in different manner and degree. In this case, the whole is called complex while articulated in dominance so that some relations may subordinate the others, affecting the system at different levels and by different instances. The case of the smart meter and the smart/stupid grid presented in Chapter 1 illustrates this idea.

The following proposition solves the demarcation problem stated in Definition 2.3.

Proposition 2.1 System demarcation and its conditions of existence A given particular system (PS) differentiates itself from everything else through a peculiar function(PF); conversely, without this function, there is no such a system. The PF, at the same time, determines the existence of that given system as such while demarcating its boundaries and relations to the environment. There are three general groups of necessary conditions for a given particular system to exist as such. They are:

1 C1 Conditions of production refer to the (physical/material) possibility that PF can be produced.

2 C2 Conditions of reproduction refer to conditions internal to PS that guarantee the recurrence of its operation to perform its PF.

3 C3 External conditions are aspects outside the PS boundaries that directly or indirectly affect C2.

From this proposition, we can derive some interesting consequences. First, the system demarcation refers only to particular realizations of systems, not systems in general; on the other hand, this demarcation approach only makes sense if a theory of systems in general (as the one postulated here) exists. Second, a particular system whose PF is physically impossible cannot exist as such (e.g. a communication system designed to work outside Shannon's limit cannot exist); however, in some particular cases, it might exist as a thought experiment to challenge such an impossibility (this is the case of Maxwell's demon to be studied later in this chapter). Third, even if such a particular system is possible, it may not exist owing to conditions internal to its operation, and thus, the system cannot be established to perform its PF (e.g. a quantum personal computer is not yet possible because of operational instabilities related to quantum phenomena that the current technology cannot solve, or the lack of personnel capable of operating a given machine). Fourth, external events may also affect the system's conditions of reproduction (e.g. an earthquake that devastates the transportation system of a given city, or the lack of investment in education). Lastly, systems are not only affected by external events but also affect what is external to them (e.g. air pollution).

The starting point to demarcate a particular system is its technical description, i.e. its components that are combined to perform a given function. However, as we have discussed, these elements and their combinations are not enough to solve the demarcation problem following Definition 2.3: we have to describe what is needed for the system to function! To make this discussion less abstract, let us return to our “car” example.

Example 2.2 Demarcating car as a system. Let us consider a particular car that already exists. In this case, we have:

1 PS Car composed of its structural, operating, and flow components (as briefly described in Example 2.1).

2 PF Convert fuel into kinetic energy that is transferred to four wheels in order to transport persons.

3 C1 It is possible to convert fuel (e.g. gasoline) into kinetic energy that can be transferred to the wheels through a mechanical structure. The engine is what allows this conversion.

4 C2 A proper maintenance of the car and its components, availability of fuel, a person capable of driving…

5 C3 Technical training for car maintenance, highways and streets with good quality, adverse conditions such as economic crisis, and extreme weather events…

As expected, PS, PF, and C1 are very well defined (although the list of the example above should be longer to be complete), while C2 and C3 could be as long as needed (but never exhaustive). The engineer or analyst task is to select C2 and C3 so that the most relevant instances and factors are included depending on the context they are dealing with.

Let us provide another example, now a new wind turbine that does not yet exist but is being designed.

Example 2.3 Demarcating a new model of a wind turbine as a system. Let us consider a different kind of wind turbine that could be used in apartment buildings. Such a system does not yet exist as a material entity but engineers have a conceptual model about it.

1 PS (a) Structural components: metal tower, new type of blades, connection to the grid; (b) operating components: power electronic devices and an electric generator; and (c) flow components: wind and electricity.

2 PF Convert kinetic energy from wind into electric energy.

3 C1 It is physically possible to convert the kinetic energy from wind into electric energy.

4 C2 The electricity generated has to be synchronized with the grid in case of alternating current (AC) with the same frequency by using power electronic devices, proper maintenance of the components, existence of wind with enough kinetic energy to allow for the power conversion, existence of protective devices against risk situations (e.g. strong winds, or overcurrent)…

5 C3 Battery storage in the building, management of electricity demand, investment programs to support renewable energy, elections, subsidies, willingness to use wind turbines, regulations and laws that allow distributed energy resources, raw material to produce such a new turbine, extreme situations like a civil war…

As before, PS, PF, and C1 are very precise, while C2 and C3 are unbounded. In this case, this particular wind turbine does not materially exist, but it is still only a conceptual system. This nevertheless indicates the main determinations that a material realization of such a wind turbine are subjected to in order to function. The differences of material and conceptual systems will be discussed in the next section.

To conclude this section, we will present a proposition that posits the importance of the demarcation process.

Proposition 2.2 Demarcation as a theoretical process The demarcation of a particular system is a theoretical process that takes as raw materials the components of the system with their respective attributes and function(s) to determine its complex articulation with the environment for a given context. Therefore, the demarcation is a purely symbolic operation with respect to such a particular system, which becomes the abstracted, purified object of a discourse that aims to be objective and true. The demarcation process thus produces objective (scientific) knowledge about the actually functioning system through (i) its purification followed by (ii) its articulation in the specific context in which it functions, or will function.

It is also important to remember that the object of knowledge (the particular system that is subjected to the demarcation) is not the same as the material object (the real existing system), and they exist in different domains. However, the demarcation, as a theoretical process performed in the object of knowledge, produces a knowledge effect on the material object in the specific environment in which it exists or will potentially exist.