KR Conference 2014 Conference Paper
versus facts that are caused (or explained) by other facts and the rules. In this context, the corresponding causal closure assumption (see. e. g., (Reiter 2001)) can be viewed as a particular form of an old philosophical principle of universal causation, which amounts to the requirement that all facts that hold in a situation should be either caused by other occurrent facts, or else preserve their truth-values in time (due to the accompanying inertia assumption). A direct incorporation of such causal assertions into the language of the situation calculus has been proposed in (Lin 1995; 1996), and has been shown to provide a natural account of both the frame and ramification problems. Subsequently, a general formal framework for this kind of causal reasoning, called a causal calculus, has been suggested in (McCain and Turner 1997). An elaborate implementation of the above causal principles in reasoning about actions has been given in (Giunchiglia et al. 2004). The formalism of (Giunchiglia et al. 2004), however, is a multi-sorted and multi-layered representation framework. As its top layer, it employs a causal action description language C+ that provides highlevel descriptions of action domains in terms of three kinds of propositional atoms (actions, simple fluents and statically determined fluents) and three different kinds of causal laws (static laws, action dynamic laws and fluent dynamic laws). Domain descriptions in this language are then instantiated by assigning temporal stamps to propositions, and incorporating the resulting descriptions into an atemporal causal calculus of (McCain and Turner 1997). The models of the resulting causal theories are viewed then as intended models of the source, higher-level action descriptions. In this study2 we will attempt to single out and ‘streamline’ the logical framework behind the language C+. To this end, we will introduce a dynamic generalization of the original causal calculus, which will be formulated, ultimately, in terms of a single basic kind of dynamic causal rules. This dynamic calculus will provide a direct and uniform logical description for the language C+. In addition, we will describe also a logical (monotonic) system of dynamic causal inference that will constitute a concise logical framework for causal reasoning in dynamic domains. We introduce dynamic causal calculus, a nonmonotonic formalism that can be viewed as a direct logical counterpart of the action description language C+ from (Giunchiglia et al. 2004). We formulate a nonmonotonic semantics of the associated causal language, and compare this semantics with the indirect, two-stage semantics for C+, given in (Giunchiglia et al. 2004). It will be shown, in particular, that the suggested semantics allows us to alleviate syntactic distinctions between propositional atoms, maintained by C+, as well as type restrictions imposed on its causal laws. We will describe also a logical formalism of dynamic causal inference that constitutes a complete description of the logic that is adequate for this dynamic calculus.