A logic-based calculus of events

We outline an approach for reasoning about events and time within a logic programming framework. The notion of event is taken to be more primitive than that of time and both are represented explicitly by means of Horn clauses augmented with negation by failure. The main intended applications are the updating of databases and narrative understanding. In contrast with conventional databases which assume that updates are made in the same order as the corresponding events occur in the real world, the explicit treatment of events allows us to deal with updates which provide new information about the past. Default reasoning on the basis of incomplete information is obtained as a consequence of using negation by failure. Default conclusions are automatically withdrawn if the addition of new information renders them inconsistent. Because events are differentiated from times, we can represent events with unknown times, as well as events which are partially ordered and concurrent.