ST/SD Lexicon

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Contents


Systems Thinking

[ A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z ]

[ A ]

animated system: systems and models in which the whole is purposeful but the parts are not. [Ackoff, RL. 1999. Ackoff's Best. Wiley, New York.]

archetypes

  • common system structures that produce characteristic patterns of behavior. (SEE ALSO: system archetypes) [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.] See also: "system archetypes".
  • the word comes from the Greek archetypos meaning "first of its kind". [Senge P, Kleiner A, Roberts C, Ross R, Smith B. 1994. The Language of Systems Thinking: "Links" and "Loops". The Fifth Discipline Fieldbook. Doubleday Currency, New York. ]

[ B ]

balancing feedback loop: a stabilizing, goal-seeking, regulating feedback loop, also known as a "negative feedback loop" because it opposes, or reverses, whatever direction of change is imposed on the system. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

bounded rationality: the logic that leads to decisions or actions that make sense within one part of a system but are not reasonable within a broader context or when seen as a part of the wider system. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

[ D ]

deterministic system: systems and models in which neither the parts nor the whole are purposeful. [Ackoff, RL. 1999. Ackoff's Best. Wiley, New York.]

[E ]

ecological system: systems and models in which the parts are purposeful but the whole is not; ecological systems contain interacting mechanistic, organismic, and social systems, but unlike social systems have no purpose of their own. [Ackoff, RL. 1999. Ackoff's Best. Wiley, New York.]

[ F ]

feedback loop

  • the mechanism (rule or information flow or signal) that allows a change in a stock to affect a flow into or out of that same stock. A closed chain of causal connections from a stock, through a set of decisions and actions dependent on the level of the stock, and back again through a flow to change the stock. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]
  • The feedback loop is the basic structural element in systems. Dynamic behavior is generated by feedback. The more complex systems are assemblies of interacting feedback loops. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p 4-5.]

feedback loop substructure: A feedback loop consists of two distinctly different types of variables - the levels (states) and the rates (actions). Except for constants, these two are sufficient to represent a feedback loop. Both are necessary. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p 4-6.]

[ H ]

hierarchy: systems organized in such a way as to create a larger system. Subsystems within systems. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

[ L ]

limiting factor: a necessary system input that is the one limiting the activity of the system at a particular moment. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

linear relationship: a relationship between two elements in a system that has constant proportion between cause and effect and so can be drawn with a straight line on a graph. The effect is additive. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

[ N ]

nonlinear relationship: a relationship between two elements in a system where the cause does not produce a proportional (straight-line) effect. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

[ R ]

reinforcing feedback loop: an amplifying or enhancing feedback loop, also known as a "positive feedback loop" because it reinforces the direction of change. These are vicious cycles and virtuous circles. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

resilience: the ability of a system to recover from perturbation; the ability to restore or repair or bounce back after a change due to an outside force. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

self-organization: the ability of a system to structure itself, to create new structure, to learn, or diversify. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

[ S ]

shifting dominance: the change over time of the relative strengths of competing feedback loops. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

social system: systems and models in which both the parts and the whole are purposeful. [Ackoff, RL. 1999. Ackoff's Best. Wiley, New York.]

suboptimization: the behavior resulting from a subsystem's goals dominating at the expense of the total system's goals. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

system: a set of elements or parts that is coherently organized and interconnected in a pattern or structure that produces a characteristic set of behaviors, often classified as its "function" or "purpose". [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

system archetypes: a formal and freestanding way of classifying structures responsible for generic patterns of behavior over time, particularly counter-intuitive behavior. ( SEE ALSO: archetypes.) [Wolstenholme, EF. 2003. A core set of archetypal structures in system dynamics. System Dynamics Review 19(1): 7-26.]

[ T ]

teleological system

  • systems that are goal seeking and purposeful; an output-oriented view of a system rather than a deterministic input-oriented view of the system. [Ackoff, RL. 1999. Ackoff's Best. Wiley, New York.]
  • taking into account what is variously and rather loosely called adaptiveness, purposiveness, goal-seeking and the like. [von Bertalanffy, L. 1969. General System Theory. George Braziller, New York.]

System Dynamics

[ A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S T | U | V | W | X | Y | Z ]


[ A ]

accumulation: the activity that takes place in a stock; the net of inflows and outflows to and from a stock. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

[ C ]

causal link: indicates a causal relationship between variables. [Richardson GP, Pugh III, AL. 1981. Introduction to System Dynamics Modeling with DYNAMO. Productivity Press, Portland.]

closed boundary

  • interactions within the system that produce[s] growth, fluctuation, and change. Any specified behavior must be produced by a combination of interacting components. Those components lie within a boundary that defines and encloses the system. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p4-1 to 4-2.]
  • In concept a feedback system is a closed system. Its dynamic behavior arises within its internal structure. Any interaction which is essential to the behavior mode being investigated must be included inside the system boundary. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p 4-2.]

[ D ]

delays: a process whose output lags behind its input in some fashion. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

dynamic equilibrium

  • the condition in which the state of a stock (its level or its size) is steady and unchanging, despite inflows and outflows. This is possible only when all inflows equal all outflows. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]
  • a stock is in equilibrium when it is unchanging (a system is in equilibrium when all its stocks are unchanging). For a stock to be in equilibrium the net rate of change must be zero, implying the total flow is just balanced by the total outflow. If water drains out of your tub at exactly the rate it flows in, the quantity of water in the tub will remain constant and the tub is in equilibrium. Such a state is termed dynamic equilibrium since the water in the tub is always changing. [Sterman, JD. 2000. Business Dynamics. Irwin McGraw-Hill, Boston.]

dynamics: the behavior over time of a system or any of its components. [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]

[ F ]

first-order negative feedback loop: Where a single decision variable (the flow) controls the input to one system level (the state variable). Where there is no delay or distortion in the information channel going from the level (the state variable) to the decision (the flow) the apparent system level is assumed identical to the actual system level. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-3.]

first-order system: a system in which there is only one level variable. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-3.]

flows

  • material or information that enters or leaves a stock over a period of time. (SEE ALSO: rates) [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]
  • terminology used in different disciplines (SEE ALSO: stocks). [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
  • mathematics, physics and engineering - derivatives, rates of change, flows
  • chemistry - reaction rates
  • manufacturing - throughput
  • economics - rates
  • accounting - flows, cash flow or income statement items
  • biology, physiology - diffusion, rates, flows
  • medicine, epidemiology - incidence, infection, morbidity and mortality rates

[ L ]

levels

  • the integration (or accumulation) of the results of actions in a system; level variables can not change instantaneously; levels create system continuity between points in time. (SEE ALSO: stocks) [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland.]
  • levels represent the condition or state of the system. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-10.]

[ M ]

modeling: a main purpose of modeling is to design and test policies for improvement.[Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

[ N ]

negative feedback loop

  • a loop in which the control decision attempts to adjust some system level to a given value by a goal introduced from outside the loop. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-9.]
  • negative loops are self-correcting; they counteract change. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

noise: apparently random and/or meaningless variation in a stream of data; what is considered noise and what is considered signal is a matter of perspective an purpose; as a matter of model scope noise might be filtered out or included as legitimate system feedback; one person's noise is another person's signal. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

[ P ]

path dependence: a pattern of behavior in which the ultimate equilibrium depends on the initial conditions and random shocks as the system evolves; path dependence arises in systems with locally unstable equilibria. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

path dependence governed by negative feedback: the greater the displacement from the equilibrium the greater the force pushing it back toward equilibrium; e.g., displace a steel ball in a bowl to the edge of the bowl and release it - it will eventually come to rest at the bottom of the bowl; disturbances do not affect the equilibrium reached. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
path dependence governed by positive feedback: the greater the displacement from the equilibrium the greater the force pushing it away from equilibrium; e.g., a steel ball disturbed from its resting place at the very top of an up-side-down bowl will pick up speed as it moves out of equilibrium; the initial disturbance determines the path taken by the ball and perhaps the ultimate destination - the system is path dependent. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

policy resistance: the tendency for interventions to be delayed, diluted, or defeated by the response of the system to the intervention itself. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

positive feedback loop

  • a positive loop diverges or moves away from a goal (unlike a negative feedback loop that seeks an externally determined goal). Action within the positive loop increases the discrepancy between the system level and a "goal" or reference point. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-16.]
  • positive loops are self-reinforcing; they tend to reinforce or amplify. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

[ R ]

rate equations: capture the decision-making processes of the agents of the physical and biological laws that cause change in system states. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

[ S ]

second-order negative feedback loop: a system with two level variables, both of which are seeking a goal. A second order negative feedback loop system is required to produce oscillation in the system (when the delay parameters are disturbed, otherwise the system may be in equilibrium). [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-10.]

second-order system: a system that has two level variables. [Forrester, JW. 1971. Principles of Systems. Productivity Press, Portland. p2-10.]

stocks

  • an accumulation of material or information that has built up in a system over time. (SEE ALSO: levels) [Meadows, DH. 2008. Thinking in systems : a primer. Chelsea Green Publishing, Vermont.]
  • characterize the state of a system and provide the basis for actions. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
  • provide systems with inertia and memory. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
  • are the sources of delays. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
  • decouple rates of flow and create disequilibrium dynamics. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
  • terminology used in different disciplines (SEE ALSO: flows). [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]
  • mathematics, physics and engineering - integrals, states. state variables, stocks
  • chemistry - reactants and reaction products
  • manufacturing - buffers, inventories
  • economics - levels
  • accounting - stocks,balance sheet items
  • biology, physiology - compartments
  • medicine, epidemiology - prevalence, reservoirs

system boundary: the delineation of system components that are necessary to generate the behavior of interest, excluding where possible, and aggregating where useful for simplicity. [Richardson GP, Pugh III, AL. 1981. Introduction to System Dynamics Modeling with DYNAMO. Productivity Press, Portland.]

[ T ]

tipping point: the point in time when the dominance of one feedback loop gives way to the dominance of another feedback loop; the first loop starts strong then declines in strength until the system passes through the point where the second loop begins building strength; a simple SIR epidemic model is an example. [Sterman, JD. 2000.Business Dynamics: Systems Thinking and Modeling for a Complex World. Irwin McGraw-Hill, Boston.]

[ V ]

variables: objects in a model that represent quantities. [Richardson GP, Pugh III, AL. 1981. Introduction to System Dynamics Modeling with DYNAMO. Productivity Press, Portland.]

variables, dependent: quantities whose value can be changed by another variable. [Richardson GP, Pugh III, AL. 1981. Introduction to System Dynamics Modeling with DYNAMO. Productivity Press, Portland.]

variables, independent:quantities whose value cannot be changed by another variable. SEE ALSO: constant, parameter.[Richardson GP, Pugh III, AL. 1981. Introduction to System Dynamics Modeling with DYNAMO. Productivity Press, Portland.]

References

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