Chapter 8 - Concurrent events

Abstract

This chapter deals with concurrent event occurrences that one might want to prohibit and methods for prohibiting them. Then, discusses concurrent event occurrences that have cumulative and canceling effects and how to handle them. The commonsense world places certain restrictions on what events can occur simultaneously. There are two methods for representing these restrictions in the event calculus: state constraints and event occurrence constraints. The first method of restricting concurrency is to use state constraints. This method relies on the fact that, if the effects of two events are inconsistent with a state constraint, then those events cannot occur concurrently. The second method of restricting concurrency is to use event occurrence constraints, or formulas involving two or more atoms of the form Happens. When several events occur at the same time, the effects of those events might differ from what the effects would have been at the events occurred at different times. Specifically, two or more concurrent events can produce new, additional effects.