International Encyclopedia of Systems and Cybernetics

"A symbolic representation of a set of objects, their relationships and their allowable motions" (P. DENNING, 1990, p.466).

DENNING explains: "We use models in three principal ways:

"Description: we sometimes use a model to describe how a system works. Examples are a blueprint, a scale model of a railroad, the equation of motion of a planet, the scientific method, and the software-design process.

"Computation: We sometimes use a model to guide, to reproduce or to calculate action in the domain. Examples are following directions from an inertial guidance system (guiding), a flight simulator (reproducing), or computing a measurement (calculating).

"Prediction: We sometimes use a model to predict the future state of a system with tolerable certainty. Examples are the models that predict the lift of a wing in flight, the position of a star or the future state of the weather or the world economy. A model is useful for prediction only if the future state can be calculated much more rapidly than in real time, and only if its users agree that the assumptions about parameter values and governing laws will hold at the future time."

This author adds: "Models are of interest because of our unavoidable concern to anticipate and prepare for future action, and because they make the world seem simpler and more understandable" (p.466).

B. ZEIGLER observes that a model that "could correctly answer every conceivable question about a real system… is not realistically constructable for large scale systems. Indeed, we assume that with every large scale system there is associated a multitude of models capable of answering only a limited set of questions about the real system with any degree of credibility" (1978, p.81).

T.F.H. ALLEN and T.B. STARR use another definition for model: "An intellectual construct for organizing experience" (1982, p.273).

J. CASTI puts it as follows: "The scientific answer to a question is a set of rules, or as such rules are more commonly termed, a model" (1994, p.4). If this is the case, specific models are mere products of more general conceptual constructs… or possibly is it the other way around

ALLEN and STARR also observe: "We generally do not extend our use of the word to include models as approximations of ontological reality. We prefer to acknowledge that we do not know what is the relationship of models to ontological reality" (Ibid).

→ Ontological skepticism