Most approaches to information modelling are so-called snapshot approaches. This means that they focus on static properties of a universe of discourse only. Some approaches consider the temporal dimension of a universe of discourse. In these approaches the concept of event is central. It is used to denote, e.g., a decision or an action which takes place at a certain time point. In this paper the concept of event is analyzed within the framework of first-order predicate logic. An axiom system for discrete time points and axiom schemes for events is presented. It is shown that the axiom schemes obtained apply to a number of cases with wide applicability. Further, several remaining problems are pointed out.