Reasoning about Actions, Narratives, and Ramification

The Language E is a simple declarative language for describing the effects of action occurrences within a given narrative, using an ontology of actions, time points and fluents (i.e. properties which can change their truth values over time). This paper shows how E may be extended to deal with ramifications. More precisely, we show how Language E domain descriptions can include statements describing permanent relationships or constraints between fluents, and how the model theoretic semantics of E can be extended in an intuitive way to ensure that the effects of actions are appropriately propagated via such statements, whilst retaining E's simple approach to the frame problem. We also show how Event Calculus style logic programs may be used to compute consequences of such domain descriptions using standard SLDNF, even when only incomplete information is given about some initial state of affairs. Because of E's generality, these techniques are easily adaptable to other formalisms for reasoning about actions, such as the Language A and the Situation Calculus