Norman McCain

Nonmonotonic causal theories

The nonmonotonic causal logic defined in this paper can be used to represent properties of actions, including actions with conditional and indirect effects, nondeterministic actions, and concurrently executed actions. It has been applied to several challenge problems in the theory of commonsense knowledge. We study the relationship between this formalism and other work on nonmonotonic reasoning and knowledge representation, and discuss its implementation, called the Causal Calculator.

Loop Checking and the Wll-Founded Semantics

Using a calculus of goals, we define the success and failure of a goal for propositional programs in the presence of loop checking. The calculus is sound with respect to the well-founded semantics; for finite programs, it is also complete. A Prolog-style proof search strategy for a modification of this calculus provides a query evaluation algorithm for finite propositional programs under the well-founded semantics. This algorithm is implemented as a meta-interpreter.