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System Dynamics Glossary

This is the System Dynamics Glossary compiled by David N. Ford and Accepted by Yaman Barlas. It was published on November 7th 2019 here: https://doi.org/10.1002/sdr.1641.

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Introduction

As a narrowly focused dictionary, this glossary defines commonly used terms that are central to traditional system dynamics and some more general terms that have special meanings or particular importance within system dynamics. General terms that have no special meanings in system dynamics, application‐specific terms, and software‐specific terms are not included. The reader is referred to the relevant literature for those definitions, as well as detailed descriptions, explanations, and examples of the terms included here.

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Click on the Concept to View the complete Description.

Concept
Description
Feedback
When the effect of a causal impact comes back to influence the original cause of that effect. A feedback loop is a sequence of variables and causal links that creates a closed ring of causal influences. See reinforcing feedback loop and balancing feedback loop.
Feedback loop polarity
A characteristic of feedback loops represented by a positive (+) or negative (−) sign that indicates whether a loop is a reinforcing (positive) or balancing (negative) one. Loop polarity is found by the algebraic product of all signs around a loop.
Flow (rate)
The movement of quantities between stocks within a system boundary or across the model boundary and thereby into or out of the system (sinks and sources); changes in stocks over time. Flows represent activity, in contrast to stocks, which represent the state of the system.
Formalization (specification)
The creation of a model from a conceptual model that can be mathematically analyzed, solved or simulated.
Frequency of oscillation
A descriptive measure of oscillatory behavior. The number of cycles a system generates in a time unit. The inverse of the period of oscillation.
Generic structure
A structure that can be applied across different settings due to having the same fundamental underlying components and relationships. See system archetype.
Goal‐seeking behavior
A behavior mode in which the system moves towards an equilibrium or target condition. The flow that changes the stock value is typically modeled as a fraction of the difference between the equilibrium condition (or target) and the current condition. Therefore, the further the system is from the goal, the more it changes towards that goal and as it approaches the goal the increase or decrease slows. The corresponding structure is associated with negative feedback. See exponential behavior.
Graphical differentiation
The process of using graphs to determine and describe the net flows that impact a stock, based on the given values of the stock over time; the complement of graphical integration.
Graphical function
A graph that relates the values of one variable to the values of another. The relation between input and output variables is plotted on a graph. Often used to describe nonlinear relationships.
Graphical integration
The process of using graphs to determine and describe how a stock changes over time, based on the behavior of its flows.
Group model building
A methodology for building models in which a group or team of people participate actively and simultaneously in building the model.
Growth with overshoot
A behavior mode in which a system increases beyond its target or equilibrium condition and then decreases. See overshoot and collapse.

References

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