COPLAS: a COnditional PLAnner with Sensing actions
Jorge Lobo · 1998
This paper describes a partial order planner written in prolog. The planner handles sensing actions, thus, generating conditional plans. Background The language A of Gelfond and Lifschitz (GL93) was designed as the basis of a high level language to represent and reason about actions and their effects. Domain descriptions written in this language define state automata that describe how situations in the world change after actions defined in the domain are executed. A has served as a platform to study the formalization of action theories. Extensions of .4 have been developed to study and reason about the concurrent execution of actions, the non-deterministic effects of some actions and to study many instances of the qualification and ramification problems. Baral at University of Texas at E1 Paso, together with his students has implemented a liner planner based on .4 (Kah96) that in many instances compares very well to standard planners such as UCPOP (BCF+95), one of the most commonly used (partial order) planners. In (LMT97) we had proposed a new action description language called .4K..4K is a minimal extension of ,4 to handle sensing actions. A sensing action is an action that does not have any effect in the world. The effect is only in the perception of the reasoning agent about the world. The execution of a sensing action will increase the agent knowledge about the current state of the world. Take for example a deactivated agent placed inside a room. The agent has duties to carry out and will be activated by a timer. Let us assume the agent is always placed facing the door. The agent, once activated, may become damaged if it attempts to leave the room since the door may be closed. Before the agent tries to leave the room it needs to perform some act of sensing in order to determine whether the door is opened or not. The agent has incomplete knowledge