REASONING ABOUT ACTIONS - STEADY VERSUS STABILIZING STATE CONSTRAINTS

In formal approaches to commonsense reasoning about actions, the Ramif ication Problem denotes the problem of handling indirect effects which implicitly derive from so-called state constraints. We pursue a new d istinction between two kinds of state constraints which will be proved crucially important for solving the general Ramification Problem. Ste ady constraints never, not even for an instant, cease being in force. As such they give rise to truly instantaneous indirect effects of acti ons. Stabilizing state constraints, on the other hand, may be suspende d for a short period of time after an action has occurred. Indirect ef fects deriving from these constraints materialize with a short lag. Th is hitherto neglected distinction is shown to have essential impact on the Ramification Problem: if stabilizing state constraints interact, then approaches not based on so-called causal propagation prove defect ive. But causal propagation, too, is shown to risk producing anomalous models, in case steady and stabilizing indirect effects are propagate d indiscriminately. Motivated by these two observations, we improve th e theory of causal relationships and its Fluent Calculus axiomatizatio n, which both are methods of causal propagation, so as to properly han dle the distinction between steady and stabilizing constraints. (C) 19 98 Elsevier Science B.V. All rights reserved.