<aside> đźš© A system is a powerful and convenient way to organize your models of real things.

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What is a System?

Virtually any real thing of interest in engineering can be modelled with systems. This provides a conceptually simple yet universal scheme for thinking about how different things interact. This also provides a starting point for developing complex and quite accurate models of how reality behaves.

For now, though, we’ll just consider the basics of how to model systems.

Definition of a System

From KMR90 and SJ00, we have the following definition of a system:

<aside> <img src="/icons/book_blue.svg" alt="/icons/book_blue.svg" width="40px" /> A system is (1) a set of (2) interacting elements, (3) that provide a specific set of transformative functions, and (4) that is distinct from its environment.

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That is, a system has four characteristics:

  1. A system has more than one part. These parts are called components or elements because they aren’t necessarily “parts” in the physical sense.
  2. A system's elements interact in some relevant way. An interaction is when two system elements exchange mass, energy, or information.
  3. A system provides a set of transformative functions. It transforms its inputs into its outputs. With respect to engineering design, we can say that the purpose of a system is to produce specific outputs from given inputs. However, not all inputs and outputs are preferred. Some inputs and outputs are not useful and may even be harmful. As engineers, we must manage both the beneficial and harmful inputs and outputs.
  4. A system is distinct from its operating environment. You can say with complete certainty whether an element is a part of the system or a part of everything else. No system element can be only partly in the system. We call “everything else” the system’s environment.

Perspective Matters

The perspective or point of view of how things are modelled matters, when deciding if a thing is or is not a system.

For instance, say a paperclip is lying on a table and the paperclip is not binding sheets of paper together.

Is the one paperclip a system?

From the perspective of the paperclip alone, it is not a system because it violates characteristics 1, 2, and 3 (above).

However, if we consider the table as well as one of the paperclips resting on it, then we do have a system.

<aside> <img src="/icons/help-alternate_yellow.svg" alt="/icons/help-alternate_yellow.svg" width="40px" /> Can you explain how all 4 characteristics are exhibited by the system containing the table and one paperclip resting on it?

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Photo by Jess Bailey on Unsplash.

Photo by Jess Bailey on Unsplash.

Note that everything changes if we start thinking about the paperclip as, say, a collection of features or even atoms. This too represents a change in perspective, but one we won’t learn about in this course.

Subsystems, Supersystems, and Co-systems

There are three other terms we use to describe one system's relationship to another system:

A subsystem is a system that is fully contained within another system.

A supersystem is a system that fully contains another system. (”Supersystem” and “subsystem” are inverses of one another.)