This article presents the theory and implementation of an artificial intelligence planner, CHICA. CHICA is a non-linear, domain independent planner based on techniques of computational logic. The representation language of the planner is Horn clause logic which is used to model event calculus, a logical theory of changing properties over time. The reasoning component is an abductive extension of SLDNF resolution for generating assumptions to prove a given goal. In event calculus, this procedure generates a plan of events and temporal relations necessary to prove the planning goal. CHICA uses domain contraints and techniques from contraint logic programming to efficiently implement inequality, as well as a specialized module to evaluate temporal relations. CHICA's generic search algorithm lets the implementor of a planning domain define a particular search strategy and specify domain heuristics to prune the search space. CHICA has solved a number of planning problems successfully: multiple robot block world problems, the assembly of a flashlight, and a room decoration problem. Extensions to classical Al-planning can be solved within the same framework, such as plan execution and replanning.

This paper presents the theory and implementation of a logic based discrete event simulation system. The representation language of the simulation is Horn clause logic. The simulation's theory of time is based on event calculus. The scheduling algorithm generates event notices for all activities that can be performed. This logic approach to discrete event simulation facilitates model validation and maintenance. For a given event schedule, analysis can be done by deriving the properties that hold true of the world at any time in the situation history. This novel approach to simulation enables classical simulation to be extended with explanation generation, decision support, planning, inductive learning and simulation of intelligent agents.>

The application of localized abductive reasoning in assembly planning with multiple robots is explained. The assembly problem is described in the event calculus using Horn clause logic. The assembly problem domain is decomposed into regions of activity, and the actions, predicates, and constraints of the planning problem are distributed over these regions. The reasoning component of the planner is abduction; the planner makes abduction steps locally within the regions, and the search algorithm shifts control from one region to another to find an overall global plan. An example is shown of a flashlight assembly problem in a robot cell with two robots that share one feeder.>