ABSTRACT
Artificial intelligence.—The idea of a qualitative representation of the world is not new, nor are attempts to reason qualitatively about the world (→REASONING AND RATIONALITY, REPRESENTATION). Well before its appearance in artificial intelligence (AI), the word qualitative was already being employed in various scientific communities (in economics in the 1960s with sign-based qualitative analysis, in ecology in the 1970s with the use of signs for effects between variables, and in dynamic system theory and automatic control [→DYNAMIC SYSTEM]). These approaches were motivated by the lack of quantitative data that would have enabled the use of conventional numerical models, by the desire to distinguish between what depends on the particular numerical configurations of a given model and what is related to the overall structural features of the system, or, sometimes, simply by the desire to find explanations that are understandable to human beings (→EXPLANATION).
