described in the model. The first step in the scientific method is to formulate a hypothesis or theory. A hypothesis is an educated guess or logical conclusion from known facts, which is then compared against all available data. If the hypothesis is found to be consistent with known facts, it is called a theory. Most theories explain observed phenomena, predict the results of future experiments, and can be presented in mathematical form. When a theory is found to be always correct over the course of many years, it is eventually referred to as a scientific law. But theories do not provide the algorithms for the construction of a model; models provide the algorithms needed to support a theory. A theory may be incompletely specified in the sense that it imposes certain general constraints.

There are many different types of models used across the scientific disciplines, although there is no uniform terminology to classify them. The most familiar are physical models, such as scale replicas. Algorithms constitute another, completely different type of model. A computer simulation is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system. Frequently, computer simulations are needed to solve a difficult set of equations describing the governing laws of the system (in the case of deterministic models) or to handle a very large amount of data and/or heuristic knowledge (in the case of data-mining-based models).1 In situations in which the underlying model is well confirmed and understood, computer experiments potentially could replace real experiments, which is especially useful when data collection is difficult and expensive. Computer simulations could also be heuristically important; for example, they may suggest new theories, models, and hypotheses based on a systematic exploration of a model’s parameter space.2,3

Several different taxonomies can be used to describe problems in corrosion science: static and dynamic, well and poorly understood, and simple and difficult. For the problems that are well understood, simple, and static, models either exist or can be readily developed to describe the corrosion behavior and to make predictions. Dynamic systems are usually more difficult to model, especially if the evolution of the dynamic behavior is poorly understood. Models can be based in some understanding of the phenomenon or can be based entirely on mined data.


P. Humphreys, Extending Ourselves: Computational Science, Empiricism, and Scientific Method, Oxford University Press, Oxford, U.K., 2004.


S. Hartmann, Models as a tool for theory construction: Some strategies of preliminary physics, pp. 49-67 in Theories and Models in Scientific Processes (W.E. Herfel, W. Krajewski, I. Niiniluoto, and R. Wójcicki, eds.), Studies in the Philosophy of the Sciences and the Humanities, Volume 44, Rodopi, The Netherlands, 1995.


S. Hartmann, The world as a process. Simulations in the natural and social sciences, pp. 77-100 in Modelling and Simulation in the Social Sciences from the Philosophy of Science Point of View (R. Hegselmann, U. Mueller, and K.G. Troitzsch, eds.), Series A: Philosophy and Methodology of the Social Sciences, Kluwer Academic Publishers, The Netherlands, 1996.

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