Reasoning with Qualitative Models

Qualitative reasoning about physical systems has become one of the most productive areas in AI in recent years, due in part to the 1984 special issue of Artificial Intelligence on that topic. My contribution to that issue was a paper entitled "Commonsense reasoning about causality: deriving behavior from structure" [9]. From my perspective, that paper laid out a research program that has continued to be productive to this day, and promises to continue well into the future. After establishing a framework for qualitative reasoning, the primary technical contribution of the paper was a simple, clear representation for qualitative structure and behavior, abstracted from ordinary differential equations. My subsequent Artificial Intelligence paper, "Qualitative simulation" [ 10 ], made that abstraction relation precise, presented the vastly improved QSIM algorithm for qualitative simulation, and used the abstraction relation to prove the soundness and incompleteness of QSIM. I will discuss developments in qualitative simulation in my retrospective on that paper [12], and concentrate here on the larger issue of reasoning with qualitative models.