Planning with constraints

Planning is a paradigmatic example of a cognitive process; it is an intentional goal-directed process which involves reasoning in an essential way. In early attempts to engineer planning systems reasoning was restricted to deduction; that is, the process of finding a plan was implemented in terms of deducing a sequence of actions which are sufficient to transform the initial state into the goal state. Subsequently, other forms of reasoning have been introduced, among them abduction, nonmonotonic reasoning and constraint solving. Below we shall briefly describe a planning system which searches for a plan using deduction, abduction and constraint solving; it can also be `enhanced´ with the facility to reason nonmonotonically in certain ways (although it is not clear whether this yields any computational advantage). The general architecture is known as IQ-PLAN and has been implemented in various versions, including one in Common Lisp and several in the constraint logic programming language Eclipse