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(2014/02/09) Civil, Environmental and Sustainable Engineering
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3.4.1.2. The Basics

The word system originates from the Greek word "synistanai," signifying to bring together or combine ("The

Systems Approach," n.d.). A system is an interconnected, interacting and interdependent set of components

that form a whole and create their own pattern of behavior. Four kinds of components are essential to each

system: elements, attributes, interconnections, and either a function (nonhuman system) or purpose (human
system). Elements (e.g. objects, parts, and variables) can be physical, abstract, or both. Interconnections are

the internal relationship between the elements. One example of an interconnection is a physical flow, such as

water flow to and from a reservoir. Another example would be an information-based link, such as informa-

tion regarding the fluctuation of water level in a reservoir which directly relates to rainfall and water con-
sumption. Usually, the latter is more difficult to notice when examining a system.

Attributes ??? stics. For instance, in a system with a water reservoir as an element, the amount of inflows

(e.g. rain) and outflows (e.g. evaporation) called the purpose or function. For example, the purpose of a hea-

ting/cooling system is to regulate and monitor the indoor environment at a consistent temperature. It is diffi-
cult to recognize the purpose (Meadows, 2008; "Core Assumptions and Statements," 2004).

Systems are surrounded by an environment. Open systems are those that dynamically exchange information,

mass or energy with their environment. In closed systems, however, mass and information do not get trans-
ferred to and from the environment. Living systems are good examples of open systems. Biological orga-

nisms continuously interchange information with their environment. The feedback from their surroundings

enables them to constantly evolve and adapt to the needs of their environment. Although most of real-world

systems are open ones, we can think of a thermometer as an example of a closed system. A thermometer does
exchange energy with the environment, yet no mass gets transferred between the thermometer and its sur-

roundings (Von Bertalanffy, 1950; Meadows, 2008).

As mentioned previously, a system produces its own characteristic set of behaviors. In some systems, this set
of behaviors is controlled and operated by a mechanism called feedback loops. A feedback loop is a closed

chain of connections that communicates the changes in a system to its different elements. By communicating

these changes, the system is able to maintain its dynamic equilibrium. For example a thermostat regulates the

temperature in a space by sensing a need for change and adapting to this change. If the room temperature

falls to a degree beneath the setting, the furnace is activated in order to make the room warmer until it rea-
ches the set temperature. Once the desired temperature is achieved, the furnace automatically shuts down. In

essence, the thermostat is acting as a link between the room temperature and the heat produced by the furna-

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