Variants of the Event Calculus

The event calculus was proposed as a formalism for reasoning about time and events. Through the years, however, a much simpler variant (SEC) of the original calculus (EC) has proved more useful in practice. We argue that EC has the advantage of being more general than SEC, but the disadvantage of being too complex and in some cases erroneous. SEC has the advantage of simplicity, but the disadvantage of being too specialised. This paper has two main objectives. The first is to show the formal relationship between the two calculi. The second is to propose a new variant (NEC) of the event calculus, which is essentially SEC in iff-form augmented with integrity constraints, and to argue that NEC combines the generality of EC with the simplicity of SEC. We argue that NEC also demonstrates the more general potential of using theories consisting of iff-definitions and integrity constraints as a new logic programming paradigm.