Event calculus

The event calculus is a logical language for representing and reasoning about events and their effects first presented by Robert Kowalski and Marek Sergot in 1986. It was extended by Murray Shanahan and Rob Miller in the 1990s. Similar to other languages for reasoning about change, the event calculus represents the effects of actions on fluents. However, events can also be external to the system. In the event calculus, one can specify the value of fluents at some given time points, the events that take place at given time points, and their effects. In the event calculus, fluents are reified. This means that they are not formalized by means of predicates but by means of functions. A separate predicate HoldsAt is used to tell which fluents hold at a given time point. For example, means that the box is on the table at time t; in this formula, HoldsAt is a predicate while on is a function. Events are also represented as terms. The effects of events are given using the predicates Initiates and Terminates. In particular, means that, if the event represented by the term e is executed at time t, then the fluent f will be true after t. The Terminates predicate has a similar meaning, with the only difference being that f will be false after t. Like other languages for representing actions, the event calculus formalizes the correct evolution of the fluent via formulae telling the value of each fluent after an arbitrary action has been performed. The event calculus solves the frame problem in a way that is similar to the successor state axioms of the situation calculus: a fluent is true at time t if and only if it has been made true in the past and has not been made false in the meantime. This formula means that the fluent represented by the term f is true at time t if: an event e has taken place: ; this took place in the past: ; this event has the fluent f as an effect: ; the fluent has not been made false in the meantime: A similar formula is used to formalize the opposite case in which a fluent is false at a given time.

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Concepts associés (7)

Problème du cadre

En informatique et philosophie, plus précisément en intelligence artificielle, le problème du cadre (frame problem en anglais) concerne la modélisation de l'effet des actions. Il s'agit d'énoncer la préservation du cadre : toutes les propriétés non modifiées par une action. Par exemple, si un robot pose une tasse sur une table, il faut non seulement spécifier que la tasse est désormais sur la table, mais aussi que la lumière reste allumée, que la table est toujours au même endroit, que le robot est toujours dans la même pièce etc.

Calcul des situations

The situation calculus is a logic formalism designed for representing and reasoning about dynamical domains. It was first introduced by John McCarthy in 1963. The main version of the situational calculus that is presented in this article is based on that introduced by Ray Reiter in 1991. It is followed by sections about McCarthy's 1986 version and a logic programming formulation. The situation calculus represents changing scenarios as a set of first-order logic formulae.

Event calculus